The ternary RE-Si-B systems (RE = Dy, Ho, Er and Y) at 1270 K: Solid state phase equilibria and magnetic properties of the solid solution REB2-xSix (RE = Dy and Ho)

Article abstract of DOI:10.1016/j.jallcom.2005.09.012

The solid state phase equilibria in the ternary RE-Si-B diagrams (RE = Dy, Ho, Er and Y) were determined at 1270 K using experimental techniques such as X-ray diffraction, scanning electron microscopy and electron probe microanalysis. In general, three ternary phases were obtained for each diagram: the line compound RE₅Si₂B₈ with tetragonal symmetry, the boron-inserted Nowotny phase RE₅Si₃B_x of Mn₅Si₃-type and the solid solution REB_2-xSi_x of AlB₂-type. Prior to this work, the binary systems RE-Si and RE-B, which form the boundary of each diagram, were also re-investigated. In addition to the structures of RE₅Si₃ (Mn₅Si₃-type, RE = Dy, Ho and Y) and Dy₃Si₄ (Ho₃Si₄-type) which were previously reported or will be presented in a forthcoming paper, the X-ray single crystal structures of RE₅Si₄ (Sm₅Ge₄-type, RE = Dy and Ho), DySi (CrB-type) and HoSi in both polymorphic modifications, i.e. the FeB- (high temperature) and CrB- (low temperature) types, were determined and are described herein. Structural relationships between members of the same series on one side, and between both forms of HoSi on the other side, are also discussed in terms of coordination polyhedra and interatomic distances. Finally, magnetic measurements were performed on the alloys REB_2-xSi_x, which in case of RE = Dy exhibit a marked increase of the magneto-crystalline anisotropy, whereas for RE = Ho a change from ferromagnetic to antiferromagnetic behaviour with increasing silicon content is encountered.

Full text of DOI:10.1016/j.jallcom.2005.09.012

Journal of Alloys and Compounds 417 (2006) 72–84
The ternary RE–Si–B systems (RE = Dy, Ho, Er and Y) at 1270 K:
Solid state phase equilibria and magnetic properties of the
solid solution REB2−xSix (RE = Dy and Ho)
a
Jerome Roger , Volodymyr Babizhetskyya,b, Thierry Guizouarna,
´
c
a
a,∗
´
Kurt Hiebl , Roland Guerin , Jean-Franc¸ois Halet
a Laboratoire de Chimie du Solide et Inorganique Mole´culaire, UMR CNRS 6511, Universite´ de Rennes 1, Institut de Chimie,
Campus de Beaulieu, Avenue du Ge´ne´ral Leclerc, F-35042 Rennes Cedex, France
b Max-Planck-Institut fu¨r Festko¨rperforschung, Heisenbergstrasse 1, Postfach 800665, D-70569 Stuttgart, Germany
c Innovative Materials Group, Universita¨t Wien, Wa¨hringerstrasse 42, A-1090 Wien, Austria
Received 21 July 2005; received in revised form 2 September 2005; accepted 6 September 2005
Available online 13 October 2005
Abstract
The solid state phase equilibria in the ternary RE–Si–B diagrams (RE = Dy, Ho, Er and Y) were determined at 1270 K using experimental
techniques such as X-ray diffraction, scanning electron microscopy and electron probe microanalysis. In general, three ternary phases were
obtained for each diagram: the line compound RE5Si2B8 with tetragonal symmetry, the boron-inserted Nowotny phase RE5Si3Bx of Mn5Si3-type
and the solid solution REB2−xSix of AlB2-type. Prior to this work, the binary systems RE–Si and RE–B, which form the boundary of each
diagram, were also re-investigated. In addition to the structures of RE5Si3 (Mn5Si3-type, RE = Dy, Ho and Y) and Dy3Si4 (Ho3Si4-type) which were
previously reported or will be presented in a forthcoming paper, the X-ray single crystal structures of RE5Si4 (Sm5Ge4-type, RE = Dy and Ho),
DySi (CrB-type) and HoSi in both polymorphic modifications, i.e. the FeB- (high temperature) and CrB- (low temperature) types, were determined
and are described herein. Structural relationships between members of the same series on one side, and between both forms of HoSi on the other
side, are also discussed in terms of coordination polyhedra and interatomic distances. Finally, magnetic measurements were performed on the
alloys REB2−xSix, which in case of RE = Dy exhibit a marked increase of the magneto-crystalline anisotropy, whereas for RE = Ho a change from
ferromagnetic to antiferromagnetic behaviour with increasing silicon content is encountered.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Rare-earth metal; Silicon; Boron; Phase diagram; X-ray diffraction; Electron microscopy; Crystal structure; Magnetic measurements
1. Introduction
the boron-inserted Nowotny phase Nd5Si3Bx of Mn5Si3-type.
With RE = Gd instead, the line compound Gd5Si2B8 of a new
structure type [3] was discovered in addition to the Nowotny
phase Gd5Si3B0.64. This result encouraged us to pursue the
investigations on the RE–Si–B systems when RE is a heavy rare-
earth metal. Our research was focused on the solid phase equi-
libria in the RE–Si–B system (RE = Dy, Ho, Er and Y) at 1270 K.
Prior to this work, the binary systems RE–Si and RE–B, which
form the boundary of each diagram, were re-investigated. Gen-
erally, all the binary phases reported in literature were confirmed
[5,6], as well as the more recently detected binary compounds
RE3Si4 of the Ho3Si4-type [7], formed via a sluggish peritec-
toidal reaction between RESi and RESi2−x [8,9]. Moreover, the
holmium silicide HoSi was encountered in both polymorphic
modifications, i.e. the FeB- and CrB-type structures.
The phase relations in the RE–Si–B systems (RE, rare-earth
metal) have not been studied in sufficient detail. Phase diagrams
were initially reported for RE = La, Ce, Er and Y at 1070 K [1,2],
which did not give evidence concerning the existence of ternary
phases, with the exception of very narrow homogeneity ranges
around some binary compositions. Recently, we have published
the isothermal sections of the ternary systems Gd–Si–B and
Nd–Si–B at the higher temperature of 1270 K [3,4]. No ternary
phases in the Nd–Si–B system were found with the exception of
∗
Corresponding author. Fax: +33 2 23 23 68 40.
E-mail address: jean-francois.halet@univ-rennes1.fr (J.-F. Halet).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.09.012

J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
73
This paper deals with the isothermal section of the ternary
RE–Si–B phase diagrams (RE = Dy, Ho, Er and Y) at 1270 K.
Crystal structures of RE5Si3 (Mn5Si3-type, RE = Dy, Ho and
Y) and Dy3Si4 (Ho3Si4-type) were reported recently or will
appear soon in the literature [9,10]. The X-ray single crystal
structures of the binary compounds RE5Si4 (Sm5Ge4- or struc-
turally related Gd5Si4-type, RE = Dy and Ho), DySi (FeB-type)
and both modifications of HoSi, i.e. the FeB- (high temperature)
and CrB-type (low temperature) structures as well as those of the
ternary phases REB2−xSix (RE = Dy and Ho) were solved and
are described herein. Structural relationships between members
of the same series on one side, and between both forms of HoSi
on the other side, are also discussed especially in terms of coor-
dination polyhedra and interatomic distances. Furthermore, the
magnetic behaviour for the alloys REB2−xSix for RE = Dy and
Ho is also reported.
solid state phase equilibria for each RE–Si–B system have been
established from a total of about 40 samples, which were stud-
ied by X-ray diffraction in combination with scanning electron
microscopy and electron probe microanalysis (EDS or WDS)
investigations.
At the reaction temperature mentioned above, the binary
compounds that form the boundary of the diagrams have
been confirmed: REB2 (AlB2-type), REB4 (ThB4-type), REB6
(CaB6-type), REB12 (UB12-type) and REB66 (ThB66-type) on
the boron side, while RE5Si3 (Mn5Si3-type), RE5Si4 (Sm5Ge4-
type), RESi (FeB- and/or CrB-type), RE3Si4 (Ho3Si4-type)
and RESi2−x (0.33 ≤ x ≤ 0.5) (AlB2-type) have been found on
the silicon side. The binary compound RESi2 (orthorhombic,
␣-GdSi2-type) has been only observed for RE = Dy and Ho,
while the high-temperature tetragonal form of the ThSi2-type,
reported in literature for Dy, Ho and Y, has never been obtained
at 1270 K [6]. For the Si–B system, at the present time, the
four phases SiBx (<3 at% Si), SiBn with 14 < n < 32, SiB6 and
SiB3 have been found [19]. The crystallographic data for all
the binary phases encountered at 1270 K during our studies on
the RE–Si–B systems (RE = Dy, Ho, Er and Y) are reported in
Table 1.
During our investigations, a lot of single crystals were iso-
lated by crushing the solidified samples, which were tested
for structure refinement. Due to the absence of precise struc-
tural data in literature so far, single crystal intensity data for
the binary compounds RE5Si4 and RESi, for RE = Dy and Ho,
were collected at ambient temperature. Thus, the crystal struc-
tures of Dy5Si4, Ho5Si4 (Sm5Ge4-type), the two polymorphic
modifications of HoSi (high temperature FeB and low tem-
perature CrB types) as well as that of DySi (CrB-type) were
determined.
Every RE–Si–B phase diagram at 1270 K is generally char-
acterized by the occurrence of three ternary phases: a line com-
pound RE5Si2B8, an interstitial phase RE5Si3Bx and a solid
solution REB2−xSix (Table 1). The line compound RE5Si2B8
of Gd5Si2B8-type structure exhibits an intergrown structure,
which is formed by the stacking of ThB4- and U3Si2-type slabs
alternating along the c axis of the tetragonal lattice [3,20]. The
crystal structures of all the RE5Si2B8 phases (RE = Dy, Ho
and Y) were recently reported [21]. On the contrary, no such
phase could be synthesized with erbium under our experimental
conditions.
The second phase RE5Si3Bx results from boron insertion in
the binary silicide RE5Si3 and belongs to the family of the well-
known Nowotny phases of Mn5Si3-type structure [22,23]. In
the ternary phase, boron atoms occupy the centres of octahedral
sites generated by one part of the rare-earth metal atoms. From
a structural point of view, the highest boron content within the
hexagonal structure was found to be equal to x = 0.64 for the
prototypical compound Gd5Si3Bx [3]. The decrease of the unit
cell volume after insertion of boron in RE5Si3 is indicative of
a somewhat stronger bonding between the interstitial boron and
the surrounding rare-earth metal atoms. The crystal structures of
the binary RE5Si3 and ternary RE5Si3Bx phases together with
their physical properties will be the subject of a forthcoming
paper [24].
2. Experimental
Polycrystalline samples were prepared from pure elements: rare-earth or
yttrium metal as ingots (purity > 99.9%), silicon (>99.99%) and boron (>99%)
as powders, all supplied by Strem Chemicals. Suitable amounts of powder and
freshly filed chips of the rare-earth or Y metal were mixed together and pressed
into pellets. Arc-melting of the samples (800 mg each) was performed on a
water-cooled copper hearth under a purified argon atmosphere with a Ti/Zr
alloy as a getter. To ensure homogeneity, the samples were turned over and
re-melted several times. Finally, to reach thermodynamic equilibrium, the as-
cast samples were sealed in evacuated silica tubes, heat treated at 1270 K for
one month and subsequently quenched in cold water. All the single crystals for
structure determination were isolated by crushing the solidified samples. They
had a metallic appearance and were non-reactive towards air.
Electron probe microanalyses (EPMA) were performed either on a Jeol JSM-
6400 scanning electron microscope by energy-dispersive spectroscopy (EDS)
of X-rays or on a Camebax SX 50 using wavelength-dispersive spectroscopy
(WDS) of X-rays (REB4, RESi, REB2C2 and/or elemental Si as standards).
AsmallpartofeachsamplewaspulverizedandanalyzedbyX-raydiffraction
(XRD) using a powder diffractometer (CPS 120 INEL) equipped with a position-
sensitive detector ranging from 6◦ to 120◦ in 2θ. Refinement of the unit cell
parameters was performed with the help of the CSD program package [11].
Single-crystal intensity data of all the binary and ternary phases were
collected at ambient temperature using a Nonius KappaCCD X-ray area-
detector diffractometer with graphite-monochromatized Mo K␣ radiation
˚
(λ = 0.71073 A). Data collection strategy was performed with the help of the pro-
gram COLLECT [12] and reflections were corrected using the program DENZO
of the KappaCCD software package [13]. A numerical absorption correction was
applied in some cases, on the basis of an optimized description of the crystal
faces [14]. Structures were solved by direct methods (SIR 97) [15] and least-
squares refinements, difference Fourier syntheses were run with SHELXL-97
or JANA 2000 program packages [16,17]. The program Diamond [18] was used
for the drawings of the structural units.
The magnetic properties were studied with a superconducting quantum inter-
ference device (SQUID) magnetometer MPMS-XL (Quantum Design) using
small amounts of polycrystalline samples. The temperature dependence of the
magnetization was measured for T = 2–300 K in an external field B = 0.1 T. The
isothermal magnetization versus applied field was performed in B = 0–5 T at
T = 5 K.
3. Results and discussion
3.1. Isothermal section of the ternary phase diagrams
The experimentally found ternary phase diagrams RE–Si–B
(RE = Dy, Ho, Er and Y) at 1270 K are presented in Fig. 1. The

74
J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
Fig. 1. Solid state phase equilibria in the ternary RE–Si–B system (RE = Dy, Y, Ho and Er) at 1270 K. Axes are in at%. Two-phase regions are dashed in grey.
The alloy REB2−xSix results from boron substitution by
sequently the tie-line REB4–RE5Si2B8 disappears. Therefore,
owing to the strong competition in the formation of both phases
RE5Si2B8 and REB2−xSix, especially when x = 0.4, the line
compound RE5Si2B8 is extremely difficult to obtain. Hence,
silicon in the diboride REB2. The solid solution REB2−xSix
extends up to x = 0.6 when RE = Ho and Er, while the x
value has been found to be less, i.e. x = 0.15 when RE = Dy
and Y. It is worth mentioning that the occurrence of the
ternary phase RE5Si2B8 is strongly related to the extent of
the solid solution REB2−xSix. Indeed, the ternary compound
RE5Si2B8 results from a peritectic reaction between the tetra-
boride REB4 and a liquid of composition close to RE5Si3. When
thesolidsolutionislessextended, thetie-linesREB4–RE5Si2B8,
RE5Si2B8–“RE5Si3” and RE5Si2B8–REB2−xSix are present as
it can be seen on the concentration profile of a bulk sam-
ple with atomic composition Dy/Si/B = 30/7/63, where the
three phases, Dy5Si2B8, DyB2−xSix and DyB4, are observed
(Fig. 2). This is, however, not the case when the solid solution
REB2−xSix is largely extended (RE = Ho and Er), and con-
Fig. 2. Concentration profile by WDS of a grain of Dy5Si2B8 surrounded by
grains of DyB4 and DyB2−xSix (composition in at% Dy/Si/B = 30/7/63).

J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
75
the temperature range for preparing the high-temperature phase
RE5Si2B8 (RE = HoandEr)isprobablyrestricted. Thebackscat-
tered electron image of a sample with atomic composition
Ho/Si/B = 27/8/65 as well as the corresponding concentration
profile show the occurrence of only two phases, i.e. the binary
HoB4 and the substituted phase HoB2−xSix (Fig. 3). In the same
manner, on the silicon side, the concentration profile of a bulk
sample with atomic composition Ho/Si/B = 37.5/37.5/25 shows
the thermodynamic equilibrium between HoB2−xSix and the
binary compounds HoSi and HoSi2−x instead of the expected
Ho3Si4 (Fig. 4). This result is consistent with the fact that this lat-
ter phase results from a sluggish peritectoidal reaction between
HoSi and HoSi2−x and needs a very long annealing time [7–9].
Since the HoB2−xSix phase is largely extended, the ternary phase
Table 1
RE–Si–B constituent phases, crystal structure and lattices parameters for RE = Dy, Ho, Er and Y
˚
Lattice parameters (A)
Phase
REB2
Type structure
Pearson symbol
Space group
RE
a
b
c
AlB2
hP3
P6/mmm
Dy
Ho
Er
Y
3.2902(3)
3.281(1)
3.265(1)
3.2875(6)
3.8472(4)
3.816(1)
3.770(1)
3.836(1)
REB4
ThB4
tP20
P4/mbm
Dy
Ho
Er
Y
7.093(1)
7.116(1)
7.071(1)
7.1023(5)
4.010(1)
4.024(1)
3.991(1)
4.0179(5)
¯
REB6
CaB6
UB12
cP7
Pm3m
Dy
Ho
Y
4.0998(5)
4.116(1)
4.1016(2)
¯
REB12
cF52
Fm3m
Dy
Ho
Er
Y
7.493(1)
7.5032(4)
7.4815(3)
7.5013(4)
¯
REB66
RE5Si3
RE5Si4
RESi
ThB66
Mn5Si3
Sm5Ge4
CrB
cF1880
hP16
oP36
oC8
Fm3c
Dy
Ho
Er
Y
23.381(4)
23.365(4)
23.436(2)
23.390(3)
P63/mcm
Pnma
Dya
Hoa
Er
8.3953(2)
8.3533(2)
8.297(1)
6.3138(2)
6.2800(2)
6.220(1)
Ya
8.4096(4)
6.3437(3)
Dya
Hoa
Er
7.3673(3)
7.3406(2)
7.306(1)
7.499(3)
14.5245(6)
14.4574(4)
14.372(8)
14.763(5)
7.6616(3)
7.6264(2)
7.600(1)
7.751(3)
Y
Cmcm
Dya
Hoa
Er
4.2438(2)
4.2313(2)
4.196(1)
4.262(1)
10.4857(6)
10.4474(5)
10.380(2)
10.528(2)
3.8151(2)
3.8054(2)
3.786(1)
3.832(1)
Y
RESi
FeB
oP8
Pnma
Cmcm
Dy
Hoa
Er
7.864(1)
7.8269(3)
7.870(4)
3.817(1)
3.8045(2)
3.800(2)
5.667(1)
5.6431(2)
5.648(3)
RE3Si4
Ho3Si4
oC20
Dya
Ho
Er
4.2107(2)
4.181(1)
4.160(1)
4.200(3)
23.892(2)
23.719(6)
23.615(5)
23.838(9)
3.8144(2)
3.792(1)
3.774(1)
3.819(2)
Y
RESi2−x
AlB2
hP3
P6/mmm
Dy
Ho
Er
Y
3.8264(3)
3.801(1)
3.7924(5)
3.840(1)
4.1168(7)
4.104(1)
4.083(1)
4.142(1)
RESi2
␣-GdSi2
oI12
tP30
Imma
Dy
Ho
4.029(1)
4.029(1)
3.932(1)
3.922(1)
13.317(2)
13.279(6)
RE5Si2B8
Gd5Si2B8
P4/mbm
Dya
Hoa,b
Ya
7.2209(2)
7.1830(2)
7.2234(2)
8.0545(3)
7.9900(3)
8.0961(3)

76
J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
Table 1 (Continued)
˚
Lattice parameters (A)
Phase
Type structure
Mn5Si3
Pearson symbol
hP16
Space group
RE
a
b
c
RE5Si3Bx
P63/mcm
Dya
Hoa
Er
8.3675(2)
8.4033(4)
8.279(1)
6.2594(2)
6.2392(2)
6.198(1)
Ya
8.4033(4)
6.3351(3)
REB2−xSix
AlB2
hP3
P6/mmm
Dya
Hoa
Er
3.3171(2)
3.4078(2)
3.392(1)
3.305(1)
3.8824(4)
3.9849(4)
3.947(1)
3.856(1)
Y
c
¯
SiB3
SiB6
SiBn
B6P
SiB6
Deriv. ␤-boron
hR14
oP280
–
R3m
6.319(5)
14.397(7)
11.0152(3)
12.713(10)
9.911(7)
23.8625(8)
c
Pnnm
4.043(3)
¯
R3m
a
Lattice constants on single crystal counter data.
Synthesis by H.F. furnace at 1870 K for 3 h.
Lattice constants from Ref. [6].
b
c
Ho5Si2B8 could never be synthesized, except under peculiar
conditions, i.e. arc-melting followed by a subsequent annealing
of the sample at 1870 K for 3 h with the help of a high frequency
furnace (sample in an arc-welded sealed tantalum crucible under
0.5 atm of argon gas) and after that slowly cooling it down to
roomtemperature. Unfortunately, forRE = Er, thisprocedurehas
not been crowned with success up to now. Consequently, one can
conclude that the existence of the ternary phase RE5Si2B8 for
the heavier rare-earth metals (RE = Er → Lu) is rather unlikely.
orthorhombic Sm5Ge4-type structure [25], but no precise atomic
coordinates can be found so far, with the exception of the very
recent paper by Mozharivskyj et al. on Er5Si4 [26]. The authors
reveal a reversible first-order phase transition in this binary
phase with a high-temperature phase adopting the orthorhombic
Gd5Si4-type structure (closely related with the Sm5Ge4-type)
[27] and a low-temperature phase with a monoclinic Gd5Si2Ge2-
type structure [28]. The heat capacity and the magnetic suscepti-
bility indicate a phase transition to occur between 205 and 235 K
while heating the sample. Both the Gd5Si4- and Sm5Ge4-types
are known to differ slightly in the atomic coordinates of met-
alloid atoms, but the shift is sufficient to modify in particular
the coordination scheme of some Si(Ge) atoms [25,27]. Indeed,
each Si atom in the structure of Gd5Si4 forms one covalent bond
3.2. Crystal structures
3.2.1. Dy5Si4 and Ho5Si4
The binary compounds RE5Si4 (RE = Dy, Ho, Er and Y)
have been previously reported in literature [6], to exhibit the
˚
with another Si atom (Si–Si distances of 2.45–2.47 A), in con-
trast to Sm5Ge4, where only half of the Ge atoms are covalently
˚
bonded to another Ge atom (Ge–Ge distance of 2.658 A).
The crystal structure determination of Dy5Si4 and Ho5Si4
confirms their isotypy with the Gd5Si4-type structure
(Tables 2–4). Indeed, all Si atoms form Si–Si pairs with Si–Si
˚
distances of 2.52–2.53 A. These distances are somewhat larger
than those measured for Gd5Si4, but remain acceptable for Si–Si
˚
single bonds (2.35 A) [29]. The crystal structures of Dy5Si4 and
Ho5Si4 can simply be considered as being built up from two
3D slabs alternating along the [0 1 0] direction (Fig. 5), the first
one of U3Si2-type while the second one is formed by rare-earth
Fig. 3. Backscattered electron image of a sample with composition in at%
Ho/Si/B = 27/8/65 showing the two phases HoB4 (black) and HoB2−xSix (grey)
(a). The corresponding concentration profile by WDS is given in (b).
Fig. 4. Concentration profile by WDS of a grain of HoB2−xSix surrounded by
grains of HoSi and HoSi2−x (composition in at% Ho/Si/B = 37.5/37.5/25).

J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
77
Table 2
mentally, it is worth noting that both structure types have been
foundforthebinarysilicideHoSiinthesamearc-meltedbuttons.
That part of the button in contact with the water-cooled copper
plate was quenched rapidly. It contained single crystals of the
FeB-type while the slowly cooled part of the button showed
single crystals of the CrB-type. It was then concluded that the
FeB-type structure is indeed a high temperature modification
and conversely that the CrB-type structure is a low tempera-
ture form, as previously mentioned in the literature. A general
overview of the monosilicides RESi was proposed by Hohnke
Crystal data, intensity collection and refinement for Dy5Si4 and Ho5Si4
Empirical formula
Molecular weight
Crystal system
Space group
Dy5Si4
Ho5Si4
924.85(1)
Orthorhombic
Pnma
937.00(1)
Orthorhombic
Pnma
Unit cell dimensions
˚
a (A)
7.3673(3)
14.5245(6)
7.6616(3)
819.8(1)
7.3406(2)
14.4574(4)
7.6264(2)
809.4(1)
˚
b (A)
˚
c (A)
3
˚
V (A )
Crystal size (mm3)
0.032 × 0.010 ×
0.010
7.493; 4
0.070 × 0.042 ×
0.011
7.690; 4
´
and Parthe [30]. They concluded that this polymorphism occurs
in several RESi binaries (RE = Dy, Ho and Er), but no structural
data on single crystals were proposed for both modifications
of a same rare-earth monosilicide. We put forward that several
of these monosilicides belonging to one or the other type were
studied from X-ray powder diffraction data [31,32] and that only
the single crystal structures of ErSi and YSi (CrB-type) were
reported in the literature so far [33,34]. The atomic coordinates,
displacement parameters and selected interatomic distances for
DySi and HoSi are given in Tables 6 and 7.
The CrB- and the FeB-type structures are characterized by
face-sharing metal trigonal prisms of AlB2-type, which are
packed in such a way that infinite prismatic rows centered by
infinite zigzag chains of metalloid atoms are observed [35,36].
Both the CrB- and the FeB-types differ only in the way these
rows are arranged with respect to each other (Fig. 6). The stack-
ing variation and structural relationship between the FeB- and
the CrB-types have been previously discussed in detail [30,37].
In the CrB-type structure, the rows of trigonal prisms develop
parallel to the ac plane along the [0 0 1] direction, while along the
b axis, two successive rows are translated each other from 1/2a,
and separated by empty metal tetrahedra and “square” pyramids.
In the more distorted FeB-type structure, the rows of trigonal
prisms propagate infinitely along the [0 1 0] direction, but in
two different orientations. Between two adjacent rows, empty
metal tetrahedra and “square” pyramids are always present.
Comparison of both modifications indicates that there is no
essential difference in the coordination number (CN) of the
holmium and silicon atoms. Indeed, the Si atom is surrounded by
sevenHoandtwoSiatomscorrespondingtoatri-cappedtrigonal
Calculated density (g cm−3); Z
Linear absorption
45.492
48.799
coefficient (mm−1
)
θ range (◦)
3.8 ≤ θ ≤ 27.5
−9 ≤ h ≤ 9
−18 ≤ k ≤ 18
−9 ≤ l ≤ 9
SHELXL; F2
9589
3.8 ≤ θ ≤ 35
−11 ≤ h ≤ 11
−23 ≤ k ≤ 23
−12 ≤ l ≤ 7
SHELXL; F2
12628
h
k
l
Refinement method
Reflections collected
Independent reflections; Rint
Reflections in refinement
(I > 2σ(I))
Number of variables
R (I > 2σ(I)); wR2
R (all data); wR2
Extinction coefficient
Goodness-of-fit on F2
971; 0.080
772
1822; 0.077
1374
47
47
0.025; 0.039
0.043; 0.042
0.00005(3)
1.04
0.031; 0.041
0.056; 0.041
0.00008(2)
1.00
3
˚
ꢀρ (min, max) (e/A )
−1.70/+1.96
−2.60/+2.97
trigonal prisms, separated by empty tetrahedral and “square”
pyramidal sites. Within the trigonal prisms sharing a common
face, the Si3 atoms form Si3–Si3 pairs, in addition to the Si1–Si2
˚
pairs of the U3Si2 slab, with Si–Si distances of 2.52 A.
Finally, the common structural character of all the binary
silicides RE5Si4 suggests the assumption that a first-order phase
transition might exist in these phases too, as observed for Er5Si4
[26].
3.2.2. DySi and HoSi
Single crystals of DySi (FeB-type) and HoSi in both modi-
fications (CrB- and FeB-types) were studied (Table 5). Experi-
Table 3
Atomic positional and isotropic displacement parameters for Dy5Si4 and Ho5Si4
a
2
˚
Compound
Dy5Si4
Atom
Wyckoff site
x
y
z
Ueq (A )
Dy1
Dy2
Dy3
Si1
Si2
Si3
4c
8d
8d
4c
4c
8d
0.35015(8)
0.02453(5)
0.31928(5)
0.2324(5)
0.9768(5)
0.1495(3)
1/4
0.01197(7)
0.18126(5)
0.17915(5)
0.3732(4)
0.8965(5)
0.4713(3)
0.0077(2)
0.0088(2)
0.0075(2)
0.0093(7)
0.0094(7)
0.0101(5)
0.09682(3)
0.87713(3)
1/4
1/4
0.9605(2)
Ho5Si4
Ho1
Ho2
Ho3
Si1
Si2
Si3
4c
8d
8d
4c
4c
8d
0.35003(5)
0.02418(3)
0.31915(3)
0.2315(3)
0.9775(3)
0.1499(2)
1/4
0.01172(4)
0.18038(3)
0.17911(3)
0.3719(3)
0.8956(3)
0.4713(2)
0.0072(1)
0.0087(1)
0.0074(1)
0.0078(4)
0.0088(4)
0.0090(3)
0.09652(2)
0.87722(2)
1/4
1/4
0.9603(1)
a
Ueq = exp[−2π2 (h2a*2U11 + ··· + 2klb*c*U23)].

78
J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
Table 4
˚
Selected interatomic distances (A) for Dy5Si4 and Ho5Si4
At. #1
Si1
At. #2
Dy5Si4
Ho5Si4
At. #1
RE1
At. #2
Dy5Si4
Ho5Si4
1Si2
2.521(5)
2.901(3)
2.950(3)
3.008(3)
3.075(2)
3.123(2)
2.521(5)
2.889(4)
2.905(3)
2.916(3)
3.136(2)
3.266(3)
2.522(5)
2.836(2)
2.855(2)
2.952(3)
3.009(2)
3.070(2)
3.074(2)
3.115(2)
2.901(3)
2.889(4)
2.950(3)
3.074(2)
3.266(3)
3.389(1)
3.387(1)
2.531(3)
2.881(2)
2.937(2)
3.002(2)
3.062(2)
3.114(3)
2.531(3)
2.874(2)
2.887(2)
2.907(2)
3.124(2)
3.244(2)
2.520(3)
2.820(2)
2.843(2)
2.942(2)
2.991(2)
3.060(2)
3.056(2)
3.107(2)
2.881(2)
2.874(2)
2.937(2)
3.056(2)
3.244(2)
3.371(1)
3.376(1)
2RE2
2RE2
1Si3
1Si3
1Si3
1Si1
1Si1
1Si2
1RE1
1RE1
1RE3
1RE3
2RE2
1RE3
1Si3
1Si3
1Si2
1Si2
1Si3
3.482(1)
3.520(1)
3.009(2)
3.070(2)
3.115(2)
3.075(2)
3.123(2)
3.136(2)
3.482(1)
3.520(1)
3.690(1)
3.766(1)
3.831(1)
3.860(1)
2.836(2)
2.855(3)
2.905(3)
2.916(3)
2.952(3)
3.008(3)
3.387(1)
3.389(1)
3.690(1)
3.693(1)
3.766(1)
3.860(1)
3.840(1)
3.476(1)
3.507(1)
2.991(2)
3.060(2)
3.107(2)
3.062(2)
3.114(2)
3.124(2)
3.475(1)
3.507(1)
3.670(1)
3.743(1)
3.821(2)
3.839(1)
2.820(2)
2.843(2)
2.887(2)
2.907(2)
2.942(2)
3.002(2)
3.371(1)
3.376(1)
3.670(1)
3.679(1)
3.743(1)
3.839(1)
3.826(2)
1RE1
1RE1
2RE3
2RE2
2RE2
1Si1
1RE1
2RE3
2RE3
2RE2
1RE1
1Si3
1RE3
1RE3
1RE3
1RE2
1RE2
1RE1
1RE2
1Si1
RE2
Si2
Si3
RE3
1Si1
RE1
1RE1
1RE1
1RE2
1RE3
1RE2
1RE2
1RE3
1Si2
1Si1
2Si3
1Si2
2RE3
2RE3
Fig. 5. Representation of the structure RE5Si4 (RE = Dy and Ho) of Sm5Ge4- (or Gd5Si4-) type. The two successive 3D slabs (right) are given in projection on the
ac plane. The body-centered cubes and empty pyramids and tetrahedra formed by the RE atoms are emphasized.

J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
79
Table 5
Crystal data, intensity collection and refinement for DySi and HoSi
Empirical formula
DySi
HoSi
HoSi
Molecular weight
Crystal system
Space group
190.59(1)
Orthorhombic
Cmcm
193.02(1)
Orthorhombic
Cmcm
193.02(1)
Orthorhombic
Pnma
Structural type
CrB
CrB
FeB
Unit cell dimensions
˚
a (A)
4.2438(2)
10.4857(6)
3.8151(2)
169.77(2)
4.2313(2)
10.4474(5)
3.8054(2)
168.22(2)
7.8269(3)
3.8045(2)
5.6431(2)
168.04(2)
˚
b (A)
˚
c (A)
3
˚
V (A )
Crystal size (mm3)
0.030 × 0.026 × 0.011
7.456; 4
44.084
0.054 × 0.024 × 0.018
7.620; 4
47.156
0.04 × 0.03 × 0.02
7.630; 4
47.156
Calculated density (g cm−3); Z
Linear absorption coefficient (mm−1
Absorption method
)
Analytical
0.3903; 0.6348
3.9 ≤ θ ≤ 42
−7 ≤ h ≤ 5
−18 ≤ k ≤ 19
−7 ≤ l ≤ 7
SHELXL; F2
2077
358; 0.035
340
10
0.016; 0.034
0.019; 0.034
0.0027(5)
1.03
Analytical
0.1567; 0.3884
3.9 ≤ θ ≤ 40
−7 ≤ h ≤ 5
−16 ≤ k ≤ 18
−6 ≤ l ≤ 5
SHELXL; F2
1847
315; 0.025
304
10
0.013; 0.030
0.014; 0.030
0.0072(7)
1.04
Analytical
0.2895; 0.4876
4.4 ≤ θ ≤ 40
−12 ≤ h ≤ 14
−6 ≤ k ≤ 6
−9 ≤ l ≤ 10
SHELXL; F2
4096
575; 0.030
511
14
0.014; 0.021
0.020; 0.021
0.0075(3)
1.06
(Tmin, Tmax
θ range (◦)
)
h
k
l
Refinement method
Reflections collected
Independent reflections; Rint
Reflections in refinement (I > 2σ(I))
Number of variables
R (I > 2σ(I)); wR2
R (all data); wR2
Extinction coefficient
Goodness-of-fit on F2
3
˚
ꢀρ (min, max) (e/A )
−1.56/+1.76
−2.94/+1.85
−1.38/+1.84
prismatic polyhedron, while the Ho atom, although CN = 15 for
both forms (8Ho + 7Si), presents a somewhat different coordina-
tion polyhedron stemming from the shift of one Si atom (Fig. 7).
Nevertheless, all the Si atoms form zigzag chains with similar
3.2.3. DyB2−xSix and HoB2−xSix
The structure determination of the substituted phases
DyB2−xSix and HoB2−xSix, for the silicon-rich limit, were also
solved on single crystals (Tables 8 and 9). The highest silicon
content has been found to be 5 at% for the Dy- and 20 at% for the
Ho-containing alloys. This value is also in good accord with the
experimental analyses on bulk samples by WDS (Figs. 2–4). In
the previous results by Chaban et al., the silicon content on bulk
samples prepared at 1070 K were found to be less than 5 at% for
the Er- and 2 at% for the Y-ternary alloys [1,2]. Our structural
results on ternary phases DyB1.85Si0.15 and HoB1.40Si0.60 con-
firm isotypism with the AlB2-type structure [39]. No defects on
the metalloid substructure were observed and the silicon atoms
substitute the boron ones in a randomly disordered manner. One
can see in Fig. 8 that the unit cell parameters increase with the Si
content, in agreement with the respective covalent radius of Si
˚
single bond Si–Si distances of 2.48–2.49 A in both structural
variants. The corresponding bonding angles within the zigzag
chains for HoSi are quite identical, i.e. 99.6◦ for the CrB and
100.2◦ for the FeB-type (Table 7).
From a theoretical point of view, it was mentioned that the
FeB-type compounds have a higher valence electron concentra-
tion (VEC) than the CrB-type ones [34]. The electron population
of the 4f- and 5d-transition shells of the rare-earth metals should
have an influence on the occurrence of either one or another of
these structural modifications. To confirm this hypothesis, theo-
retical calculations for both modifications of HoSi are currently
in progress [38].
Table 6
Atomic positional and isotropic displacement parameters for DySi and HoSi
a
2
˚
Compound
Atom
Wyckoff site
x
y
z
Ueq (A )
DySi (CrB-type)
Dy
Si
4c
4c
0
0
0.1409(1)
0.4234(1)
1/4
1/4
0.0057(1)
0.0067(2)
HoSi (CrB-type)
Ho
Si
4c
4c
0
0
0.1409(1)
0.4230(1)
1/4
1/4
0.0053(1)
0.0061(2)
HoSi (FeB-type)
Ho
Si
4c
4c
0.3209(1)
0.4616(1)
1/4
1/4
0.3851(1)
0.8695(2)
0.0052(1)
0.0061(2)
a
Ueq = exp[−2π2(h2a*2U11 + ··· + 2klb*c*U23)].

80
J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
Table 7
◦
˚
Selected interatomic distances (A) and angles ( ) for DySi and HoSi
At. #1
Si
At. #2
DySi (CrB-type)
HoSi (CrB-type)
At. #1
Si
At. #2
HoSi (FeB-type)
2Si
2.494(1)
2.932(1)
2.963(1)
3.115(1)
2.932(1)
2.963(1)
3.115(1)
3.517(1)
3.658(1)
3.815(1)
2.492(2)
2.923(1)
3.947(1)
3.107(1)
2.923(1)
2.947(1)
3.107(1)
3.505(1)
3.647(1)
3.805(1)
2Si
2.480(1)
2.918(1)
2.929(1)
2.947(1)
3.111(1)
3.135(1)
2.918(1)
2.929(1)
2.947(1)
3.111(1)
3.135(1)
3.580(1)
3.628(1)
3.805(1)
4RE
1RE
2RE
4Si
1Si
2Si
2RE
4RE
2RE
2Ho
2Ho
1Ho
1Ho
1Ho
2Si
2Si
1Si
1Si
1Si
RE
Ho
4Ho
2Ho
2Ho
Si–Si–Si
99.80(3)
99.59(3)
100.2(1)
3.3.1. The solid solution DyB2−xSix
˚
˚
(1.17 A) and B (0.87 A) [29]. The average metalloid–metalloid
In Fig. 9, the magnetization M(T) curves for the three com-
pounds with x values equal to 0, 0.09 and 0.15 are presented
in increasing and decreasing temperatures. Silicon substitution
for boron has indeed a remarkable influence on the magnetic
behaviour in the ordered state. The ordering temperatures TC
decrease slightly with increasing x (Table 10). However, we
observe a pronounced influence on the magneto-crystalline
anisotropy. The M(T) plots for the zero field cooled samples
(zfc) resemble the typical shape of narrow domain wall ferro-
magnets. The origin of the presence of narrow walls is a high
magneto-crystalline anisotropy energy resulting from crystal
field interactions of rare-earth moments containing an orbital
contribution, comparable in magnitude with the magnetic cou-
pling energy [42]. The magnetization values increase by thermal
activation of wall movement, pass through maxima or plateaus
and decrease near the ordering temperatures (Figs. 9b and c).
Measurements of M(T) in decreasing temperatures (field cooled,
fc) hence result in a much higher net magnetization at the lowest
temperature (2 K).
˚
˚
distances of 1.92 A (Dy) and 1.97 A (Ho) are well comprised
˚
˚
between those of HoB2 (1.89 A) and HoSi2−x, x ∼ 0.4, (2.24 A),
both adopting the AlB2-type structure. In the metalloid sub-
structure, each atom adopts a sp2-type coordination mode with
respect to the bonding angles of 120◦.
3.3. Magnetic properties
The magnetic susceptibilities for the phases REB2−xSix
(RE = Dy and Ho) have been measured in a moderate exter-
nal field B = 0.1 T in the temperature range T = 2–300 K. All
samples were polluted with traces of secondary phases, so in
single field measurements the influence of impurities cannot be
excluded (Honda–Owen plot) [40]. Thus, the derived values for
the effective moments vary slightly from the ideal tri-positive
ion moment µeff = 10.6 ␮ for either compound, but are still
B
within the errors. Since the results of the paramagnetic regime
were considered of minor interest in our study, we just present
the data of µeff and θp in Table 10, as calculated.
Fig. 6. Representation of the structure RESi (Dy and Ho) of CrB-type (a) and HoSi of FeB-type (b). The rows of infinite silicon zigzag chains are emphasized.

J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
81
Table 8
Crystal data, intensity collection and refinement for DyB2−xSix and HoB2−xSix
Empirical formula
Molecular weight
Crystal system
Space group
DyB2−xSix (x = 0.15)
186.89(1)
Hexagonal
P6/mmm
HoB2−xSix (x = 0.60)
196.92(1)
Hexagonal
P6/mmm
Unit cell dimensions
˚
a (A)
3.3171(2)
3.8824(4)
36.995(5)
3.4078(2)
3.9849(4)
40.077(5)
˚
c (A)
3
˚
V (A )
Crystal size (mm3)
0.045 × 0.032 × 0.007
9.525; 1
50.610
0.025 × 0.020 × 0.012
8.893; 1
49.463
–
–
6.9 ≤ θ ≤ 39.6
−6 ≤ h ≤ 3
−6 ≤ k ≤ 6
−7 ≤ l ≤ 7
SHELXL; F2
648
73; 0.032
73
7
Calculated density (g cm−3); Z
Linear absorption coefficient (mm−1
Absorption method
)
Analytical
0.0011; 0.0203
5.2 ≤ θ ≤ 36.6
−3 ≤ h ≤ 5
−5 ≤ k ≤ 5
−6 ≤ l ≤ 6
SHELXL; F2
630
58; 0.052
58
7
0.016; 0.036
0.016; 0.036
0.16(3)
(Tmin, Tmax
θ range (◦)
)
h
k
l
Refinement method
Reflections collected
Independent reflections; Rint
Reflections in refinement (I > 2σ(I))
Number of variables
R (I > 2σ(I)); wR2
R (all data); wR2
Extinction coefficient
Goodness-of-fit on F2
0.007; 0.016
0.007; 0.016
0.28(2)
1.09
−0.92/+0.86
1.02
−1.92/+1.06
3
˚
ꢀρ (min, max) (e/A )
The enhancement of the magneto-crystalline anisotropy is
also evidenced in the isothermal magnetization M(B) curves at
5 Kfrom insetsof Fig. 9. Thehysteresisloopbecomesmore open
with increasing x. Hence, the remnant magnetization, Mr, and
the coercive (critical) field increase with x, whereas the values of
the saturation moment decrease (Table 10). The energy product
(B·H) and consequently the magnetic hardness improves with
silicon content.
3.3.2. The solid solution HoB2−xSix
HoB2 is a simple ferromagnet at TC = 15–20 K [42]. The
zfc sample magnetization versus temperature passes a maxi-
mum whereas the fc magnetization remains constant below TC
as shown in Fig. 10a. The domain wall thickness is obviously
large, which leads to a narrow hysteresis loop and a small rem-
nant magnetization as it can be seen in the inset of Fig. 10a and
Table 10.
Table 9
Atomic positional, displacement parameters and selected interatomic distances
˚
(A) for DyB2−xSix and HoB2−xSix
DyB2−xSix (x = 0.15)
HoB2−xSix (x = 0.60)
RE
x
0
0
1a
y
0
0
z
Ueq
0
0
a
a
0.0072(3)
0.0051(1)
B, Si
2b
x
y
z
Ueq
τb
1/3
2/3
1/2
0.010(2)
0.92(3)
1/3
2/3
1/2
0.009(1)
0.70(2)
RE
12B, Si
6RE
2RE
2.7269(2)
3.3171(2)
3.8824(4)
2.8002(2)
3.4078(2)
3.9849(4)
B, Si
3B, Si
6RE
1.9151(2)
2.7269(2)
1.9675(1)
2.8002(2)
a
Ueq = exp[−2π2(h2a*2U11 + ··· + 2 klb*c*U23)].
Fig. 7. Coordination polyhedra for the Si (black) and RE (white) atoms in the
CrB- (a) and FeB-type (b) structures.
b
Boron content in the mixed position (B, Si).

82
J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
Table 10
Magnetic data for the compounds REB2 and REB2−xSix (RE = Dy, Ho)
Compound
DyB2
µeff (␮B)
θp (K)
TC (K)
TN (K)
µS (␮B)
Mr (Am2/kg)
Bcrit. (T)
Ref.
10.7
11.3a
33
14
55
55
–
–
5.4
7.9
–
10.4
–
0.05
[41,42]
b
10.1a
10.5a
40
34
52
49
–
–
6.7
6.1
20.0
22.1
0.10
0.20
b
b
DyB1.91Si0.09
DyB1.85Si0.15
HoB2
10.2
11.2a
25
30
15
20
–
–
7.5
8.5
–
8.9
–
0.05
[41,42]
b
10.6a
−6.4
–
12
6.0
0
–
b
HoB1.4Si0.6
a
Data not corrected for impurities.
This work.
b
Silicon substitution in the diboride has a dramatic conse-
quence for the magnetic behaviour (Fig. 10b). As both zfc and
fc M(T) plots pass a maximum, we suggest that HoB1.4Si0.6 is an
´
antiferromagnet at a Neel temperature TN = 12 K. This finding
corroborates with a negative value of θp. Looking at the isother-
mal magnetization M(B) curve at T = 5 K (inset of Fig. 10b),
a linear field dependence up to about B = 1.5 T is observed,
which is then followed by a metamagnetic-like transition and
finally M(B) tends to saturate in high fields. The value of the
saturation moment is reduced when compared with the one of
the pure binary compound (Table 10). Furthermore, the mag-
netization is fully reversible in decreasing field which proves
that HoB1.4Si0.6 is indeed a metamagnet. A similar alteration
Fig. 8. Variations of the unit cell constants as a function of x in the substitution
solid solution HoB2−xSix.
Fig. 9. Magnetization versus temperature in applied field B = 0.1 T for DyB2 (a), DyB1.91Si0.09 (b) and DyB1.85Si0.15 (c) (open circles, zfc and filled symbols, fc).
Inset: Isothermal magnetization versus external field (open circles, field up and filled symbols, field down).

J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
83
Acknowledgments
The authors acknowledge support from the Austrian
¨
(OAD)—French (MAE) Amadeus exchange program under
projects 9/2005 (Austria) and 08940YH (France). They also
thank J. Bauer for fruitful discussions, T. Roisnel (CDIFX, Uni-
´
versite de Rennes 1) for X-ray intensity data collection, as well
´
as J. Le Lannic (CMEBA, Universite de Rennes 1), and M. Bohn
(IFREMER, Brest) for their assistance in SEM and EPMA stud-
ies.
References
[1] Yu.B. Kuz’ma, N.F. Chaban, Binary and Ternary Systems Containing
Boron, Metallurgiya, Moscow, 1990 (in Russian).
[2] N.F. Chaban, Yu.B. Kuz’ma, Inorg. Mater. 36 (2000) 882.
[3] V. Babizhetskyy, J. Roger, S. De´putier, R. Jardin, J. Bauer, R. Gue´rin,
J. Solid State Chem. 177 (2004) 415.
[4] J. Roger, V. Babizhetskyy, R. Jardin, J.-F. Halet, R. Gue´rin, J. Alloys
Compd., in press.
[5] T.B. Massalski, Binary Alloy Phase Diagrams, second ed., ASM, Mate-
rials Park, OH, 1990.
[6] P. Villars, L.D. Calvert, Pearson’s Handbook of Crystallographic Data
for Intermetallic Phases, second ed., ASM, Materials Park, OH, 1991.
[7] I. Ijjaali, G. Venturini, B. Malaman, J. Alloys Compd. 269 (1998) L6.
[8] V.N. Eremenko, K.A. Meleshevich, Y.I. Buyanov, P.S. Martenyuk, Ukr.
Khim. Zhurn. 60 (7–8) (1994) 544.
[9] J. Roger, T. Guizouarn, K. Hiebl, J.-F. Halet, R. Gue´rin, J. Alloys
Compd. 394 (2005) 28.
[10] J. Roger, V. Babizhetskyy, K. Hiebl, J.-F. Halet, R. Gue´rin, J. Alloys
Compd., in press.
Fig. 10. Magnetization versus temperature in applied field B = 0.1 Tfor HoB2 (a)
and HoB1.4Si0.6 (b) (open circles, zfc and filled symbols, fc). Inset: Isothermal
magnetization versus external field (open circles, field up and filled symbols,
field down).
[11] L.G. Aksel’rud, P.Yu. Zavalin, Yu.N. Grin, V.K. Pecharski, B. Baum-
garter, E. Wo¨lfel, Mater. Sci. Forum 335 (1993) 133.
[12] COLLECT: KappaCCD software, Nonius BV, Delft, The Netherlands,
1998.
[13] Z. Otwinowski, W. Minor, in: C.W. Carter Jr., R.M. Sweet (Eds.), Meth-
ods in Enzymology, vol. 276, Academic Press, New York, 1997, p. 307.
[14] J. de Meulenaar, H. Tompa, Acta Crystallogr. A 19 (1965) 1014.
[15] A. Altomare, M.C. Burla, M. Camalli, B. Carrozzini, G.L. Cascarano,
C. Giacovazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Rizzi,
Acta Crystallogr. A 32 (1999) 115.
of magnetic ordering was previously reported for Ho3C4−xBx
(x < 0.8), but boron insertion in this case changes the pure binary
antiferromagnetic carbide into a ferromagnetic compound
[43].
4. Conclusion
[16] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
[17] V. Petrichek, M. Dusek, JANA 2000, Program for Crystal Structure
Refinement, Institute of Physics, Academy of Sciences of the Czech
Republic, Prague, 1998.
[18] K. Brandenburg, Diamond, Version 2.0, 1998.
[19] J. Roger, V. Babizhetskyy, J.-F. Halet, R. Gue´rin, J. Solid State Chem.
177 (2004) 4167.
[20] V. Babizhetskyy, J. Roger, S. De´putier, R. Gue´rin, R. Jardin, J. Bauer,
K. Hiebl, C. Jardin, J.-Y. Saillard, J.-F. Halet, Angew. Chem. Int. Ed.
43 (15) (2004) 1979.
[21] J. Roger, V. Babizhetskyy, S. Cordier, J. Bauer, K. Hiebl, L. Le Polle`s,
S.H. Ashbrook, J.-F. Halet, R. Gue´rin, J. Solid State Chem. 178 (2005)
1854.
[22] R. Kieffer, F. Benesovsky, B. Lux, Planseeber. Pulvermet. 4 (1956) 30.
[23] H. Nowotny, F. Benesovsky, in: P.S. Rudman, J. Stringer, R.I. Jaffee
(Eds.), Phase Stability in Metals and Alloys, McGraw-Hill, NY, 1966.
[24] J. Roger, K. Hiebl, V. Babizhetskyy, J.-F. Halet, R. Gue´rin, J. Alloys
Compd., on line.
[25] G.S. Smith, Q. Johnson, A.G. Tharp, Acta Crystallogr. 22 (1967) 269.
[26] Y. Mozharivskyj, A.O. Pecharsky, V.K. Pecharsky, G.J. Miller, K.A.
Gschneider Jr., Phys. Rev. B 69 (2004) 144102.
The solid state phase equilibria in the ternary RE–Si–B dia-
grams (RE = Dy, Ho, Er and Y), determined at 1270 K, show the
occurrence of three ternary phases: a line compound RE5Si2B8,
not found at present with RE = Er, a boron-inserted Nowotny
phaseRE5Si3Bx andasubstitutionphaseREB2−xSix. Thebinary
phases that form the boundary of each diagram have also been re-
investigated. The crystal structures of RE5Si4 (Sm5Ge4-type),
DySi (CrB-type) and HoSi in the two polymorphic modifica-
tions (FeB- and CrB-types), as well as the alloys within the
silicon-rich limits of the solid solution REB2−xSix with the
AlB2-type (RE = Dy and Ho) have been determined. Besides,
it has been demonstrated that the occurrence of the compound
RE5Si2B8 is strongly depending on the extent of the solid
solution REB2−xSix. Finally, magnetic measurements on the
substitution phases REB2−xSix lead to a marked increase of
the magneto-crystalline anisotropy with RE = Dy with increas-
ing silicon content, whereas a change from ferromagnetic to
antiferromagnetic behaviour is observed in the solid solution
HoB2−xSix.
[27] J.E. Iglesias, H. Steinfink, J. Less-Common Met. 26 (1972) 45.

84
J. Roger et al. / Journal of Alloys and Compounds 417 (2006) 72–84
[28] Y. Mozharivskyj, A.O. Pecharsky, V.K. Pecharsky, G.J. Miller, J. Am.
Chem. Soc. 127 (2005) 317.
[37] K. Schubert, Kristallstrukturen ZweiKomponentiger Phasen, Springer,
Berlin, 1964.
[29] L. Pauling, Nature of the Chemical Bond, third ed., Cornell University
Press, Ithaca, NY, 1960.
[38] M. Ben Yahia, X. Rocquefelte, J.-Y. Saillard, J.-F. Halet., unpublished
results.
[30] D. Hohnke, E. Parthe´, Acta Crystallogr. 20 (1966) 572.
[31] E.I. Gladyshevskii, P.I. Kripyakevich, Zh. Strukt. Khim. 5 (1964)
853.
[32] E. Parthe´, Acta Crystallogr. 12 (1959) 559.
[33] O. Schob, E. Parthe´, Acta Crystallogr. 19 (1965) 214.
[34] A. Raman, H. Steinfink, Acta Crystallogr. 22 (1967) 688.
[35] R. Kiessling, Acta Chem. Scand. 3 (1949) 595.
[36] T. Bjurstrom, Arkiv Kemi, Mineral. Geol. 11A (1933) 1.
[39] W. Hofmann, W. Ja¨niche, Z. Phys. Chem. B31 (1936) 214.
[40] K. Honda, Ann. Physik 32 (1910) 1027.
[41] K.H.J. Buschow, in: V.I. Matkovich, P. Hagenmuller, G.V. Samsonov,
T. Lundstro¨m (Eds.), Boron and Refractory Borides, Springer, Berlin,
1977, p. 494.
[42] K.H.J. Buschow, in: E.P. Wohlfarth (Ed.), Ferromagnetic Materials, vol.
1, North-Holland PC, Amsterdam, 1980, p. 283.
[43] E. Bidaud, K. Hiebl, J. Bauer, J. Alloys Compd. 279 (1998) 97.