Structural features of nanocrystalline holmium oxide prepared by the thermal decomposition of organic precursors

Article abstract of DOI:10.1016/j.jallcom.2014.02.123

Powders of nanostructured holmium oxide (C-Ho₂O₃) with the crystallite sizes ranging from 6 to 16 nm have been prepared in bulk from the thermal decomposition of holmium acetate and carbamide-containing complex of holmium as precursors at 600 and 700 C. The powders obtained have been investigated by X-ray diffraction, TEM, thermogravimetry, IR- and Raman spectroscopy. A comparison has been drawn between these and powdered holmium oxide with micron-sized crystallites prepared from the thermal decomposition of holmium chloride. The bcc lattice parameter of the oxides has been found to increase when the crystallite size decreases. It has been noted that the surface of air-exposed powders of holmium oxides is covered by products formed due to the chemisorption of atmospheric CO₂ and H₂O molecules.

Full text of DOI:10.1016/j.jallcom.2014.02.123

Journal of Alloys and Compounds 601 (2014) 31–37
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Structural features of nanocrystalline holmium oxide prepared
by the thermal decomposition of organic precursors
a
a
a
b
c,
⇑
M.N. Abdusalyamova , F.A. Makhmudov , E.N. Shairmardanov , I.D. Kovalev , P.V. Fursikov
,
d
c
I.I. Khodos , Y.M. Shulga
Institute of Chemistry of Tajik Academy of Science, Ajni Str. 299/2, 734063 Dushanbe, Tajikistan1
Institute of Structural Macrokinetics and Materials Science of RAS, 142432 Chernogolovka, Moscow Region, Russia
Institute of Problems of Chemical Physics of RAS, 142432 Chernogolovka, Moscow Region, Russia
Institute of Microelectronics Technology and High-Purity Materials of RAS, 142432 Chernogolovka, Moscow Region, Russia
a
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 January 2014
Received in revised form 19 February 2014
Accepted 20 February 2014
Available online 28 February 2014
2 3
Powders of nanostructured holmium oxide (C-Ho O ) with the crystallite sizes ranging from 6 to 16 nm
have been prepared in bulk from the thermal decomposition of holmium acetate and carbamide-contain-
ing complex of holmium as precursors at 600 and 700 °C. The powders obtained have been investigated
by X-ray diffraction, TEM, thermogravimetry, IR- and Raman spectroscopy. A comparison has been drawn
between these and powdered holmium oxide with micron-sized crystallites prepared from the thermal
decomposition of holmium chloride. The bcc lattice parameter of the oxides has been found to increase
when the crystallite size decreases. It has been noted that the surface of air-exposed powders of holmium
Keywords:
Holmium oxide
Synthesis
Nanostructure
Lattice parameter
Lattice expansion
crystallite size effect
2 2
oxides is covered by products formed due to the chemisorption of atmospheric CO and H O molecules.
Ó 2014 Elsevier B.V. All rights reserved.
1
. Introduction
especially versatile (sol–gel technique, for example), because these
techniques enable the controlled production of a relatively large
amount of the target material. Furthermore, low decomposition
temperatures are favorable for the formation of nanocrystalline
metal oxides, which can be pivotal to diverse practical applications
of these compounds [6–8].
While there have been a number of suitable precursors for the
2 3
formation of Ln O from the thermal decomposition of their salts,
including both inorganic such as nitrates, chlorides, sulfates, fluo-
rides and hydroxides, and organic such as carbonates, oxalates,
and acetates [9,10], for the preparation of Ho O , however, only ni-
2 3
2 3
Like other lanthanide sesquioxides (Ln O ), holmium oxide,
2 3
Ho O , finds its use in various optical, ceramic, and chemical appli-
cations, including glasses to transmit radiation for wavelength-cal-
ibration instruments [1] and pyrolysis catalysts, where holmium
oxide has been reported to exhibit surface bifunctional, acid–base
properties [2]. Nanocrystalline microstructure in this solid is of
particular interest, since we may expect that when the crystallite
size decreases down to nanometer scale, the ratio of surface to bulk
atoms increases substantially to endow materials based on hol-
mium oxide with novel features.
For the preparation of nanocrystalline lanthanide oxides a vari-
ety of techniques, both physical and chemical ones, have been
developed (see for example [3–5] and references therein). Among
the latter those that involve the thermal decomposition of precur-
sors of the metal oxides as a part of the synthesis process are
trate at 660 °C [11], carbonate at 700 °C [12,13], and oxalate at
740 °C [11] or 735 °C [14,15] have been so far reported to be
decomposed.
In the present study, nanocrystalline powders of holmium oxide
have been prepared in bulk from the thermal decomposition of or-
ganic precursors, such as holmium acetate and carbamide-contain-
ing complex of holmium at temperatures comparable to those
mentioned above. The materials obtained have been characterized
and investigated with respect to their phase composition, mor-
phology and particle size by means of X-ray diffraction (XRD),
IR- and Raman spectroscopy, elemental and thermal analysis, and
high-resolution transmission electron microscopy (HRTEM). In this
⇑
Corresponding author. Address: Institute of Problems of Chemical Physics of
RAS, Prospekt Akademika Semenova 1, 142432 Chernogolovka, Russia.
Tel./fax: +7 49652 25401.
E-mail addresses: i2212@yandex.ru (I.D. Kovalev), fpv@icp.ac.ru (P.V. Fursikov),
khodos@iptm.ru (I.I. Khodos), shulga@icp.ac.ru (Y.M. Shulga).
1
amahsuda@mail.ru.
http://dx.doi.org/10.1016/j.jallcom.2014.02.123
0
925-8388/Ó 2014 Elsevier B.V. All rights reserved.

3
2
M.N. Abdusalyamova et al. / Journal of Alloys and Compounds 601 (2014) 31–37
Table 1
Synthesis conditions for the powdered samples of holmium oxide under study.
All the four powdered samples had yellowish-white appearance in daylight.
They were additionally examined for purity by X-ray fluorescent analysis on a
COMITA X-Art M energy dispersive spectrometer. The spectrometer was equipped
with a silver anode X-ray tube as the source of exciting radiation and with a lithium
drifted silicon, Si(Li), detector. To attribute the observed peaks to the corresponding
characteristic X-ray transitions we referred to X-ray spectroscopy handbooks
Sample number Precursor
Tsynthesis (°C)
1
2
3
4
Holmium acetate
Holmium acetate
Carbamide-containing complex of Holmium 700
Holmium chloride 600
600
700
[
23,24]. The X-ray fluorescence spectrum of holmium oxide synthesized via the ace-
tate route (Fig. 1) indicates that, except for holmium, the mass content of metals
with atomic number more or equal than that of magnesium is no more than 0.1%
for every element. The precedently described synthesis procedures for the samples
of holmium oxide suggest that the X-ray fluorescence data obtained for the sample
2
are applicable to the three others.
Elemental C, H, N (by combustion method) and O (by pyrolysis method) analy-
paper we also report some observations relating to a crystallite size
effect in the samples of holmium oxide.
sis was conducted with the use of an Elementar CHNS/O Vario Micro cube analyzer.
Thermal gravimetry and differential scanning calorimetry were carried out on a
Netzsch STA 409 LUXX thermal analyzer at a heating rate of 10 °C/min in argon
or air flow.
X-ray diffraction patterns were obtained at room temperature using a powder
h–h Bragg–Brentano diffractometer ARL X’TRA with Cu radiation. The diffractometer
was equipped with a solid-state X-ray Peltier detector enabling substantially in-
creased peak to background ratio and optimized angular and energy resolution
without using b-filters and monochromators.
The average crystallite size of holmium oxides was assumed to be equal to the
mean coherent scattering domain size along the crystallographic axis [111] in hol-
mium oxide, which, in turn, was estimated by employing the Scherrer equation,
using the (222) peak in the X-ray diffraction patterns of holmium oxides:
There is an interesting effect of the crystallite size in nanocrys-
talline solids, namely these materials exhibit a significant change
in the lattice parameter with a reduction of the crystallite size from
the micro- to the nanometer scale. There have been a number of
studies addressing this effect [16–21]. Regarding to binary metal
oxides, earlier, for instance, we reported the dependence of the lat-
tice parameter on the crystallite size of titanium dioxide [22]. In
this respect, rare earth oxides and, in particular, holmium oxide,
have been given the lack of attention from researchers. Thus, an-
other aim of this paper is to attempt a correlation between the
crystallite size and the lattice parameter of holmium oxide.
d ¼ kk=b cos
H
2
. Experimental
where d – the average crystallite size, k – wavelength k (Cu Ka) = 1.54051 Å, (b – the
Nanocrystalline powders of holmium oxide were synthesized by two methods.
full width at half maximum (FWHM) of the peak (222), – diffraction angle, k = 1.
H
Method 1 (acetate route): 2 g of commercially obtained 99.99% purity holmium
oxide were added to 15 ml of nitric acid, 63.2% and 15 ml of acetic acid, 70%, stirred
until completely dissolved, and evaporated dry in air. The obtained precipitate was
air-calcined for 1 h at 600 and 700 °C (samples denoted as 1 and 2, respectively, in
Table 1). Method 2 (carbamide route) differs from the Method 1 by that the starting
holmium oxide was dissolved in 30 ml of concentrated nitric acid added with 4 g of
carbamide. The calcination was carried out in air at 700 °C (sample 3 in Table 1).
For reference purposes an additional sample (4) was prepared by using hol-
mium chloride as precursor. The starting hydrolysis mixture was obtained accord-
The value of b was calculated taking into account instrumental diffraction line
broadening which was determined using Si standard powder. It is noteworthy that
for the purposes of the estimation we considered the microstrain contribution to
the broadening to be small as compared with the crystallite size effect.
ꢀ
1
IR spectra were registered in the range of wavelengths 4000–675 cm on a Per-
kin-Elmer Spectrum 100 spectrometer with UATR accessory. Raman spectra were
recorded using a NXT FT-Raman 9650 spectrometer with an excitation laser wave-
ꢀ
1
length of 976 nm. The spectral resolution was 4 cm for the both techniques.
The microstructure of the samples was studied with the use of high resolution
transmission electron microscope Jeol JEM-2100 operating at an accelerating volt-
age of 200 keV. All the specimens for TEM/HRTEM observations were prepared as
follows. The powders of holmium oxide were thoroughly ground by hand in an
agate mortar with a pestle, then the powder particles were dispersed in ethanol
by ultrasonic treatment, drops of the suspension were deposited onto a holey car-
bon film supported on a copper TEM grid and allowed to dry in air.
ing to the reaction 2HoCl
by NaOH to bring pH to 3.6–3.8, in a cooled flask at a temperature no higher than
0 °C. The obtained slurry was placed in a glassy carbon crucible and evaporated
3 2 2 3
+ H O = Ho O + 6HCl with the following neutralization
6
dry on a stove with constant stirring. The resulting mass after being air-calcined
at 600 °C for 1 h was washed on a Büchner funnel until NaCl had been completely
removed.
Fig. 1. X-ray fluorescence spectrum of holmium oxide (sample 2, Table 1). The observed characteristic X-ray dipole transitions of holmium are also schematically represented
in the inset (as a part of the Grotrian diagram). Peaks in the spectra and the transitions are labeled according to the IUPAC and Siegbahn’s notations. The correspondence
between them can be found elsewhere [44]. Ag(La) peak occurs due to the partial elastic scattering of the incident X-ray beam from the sample.

M.N. Abdusalyamova et al. / Journal of Alloys and Compounds 601 (2014) 31–37
33
Fig. 2. Powder X-ray diffraction patterns of the well-crystallized (1) holmium oxide
and nanostructured (2) holmium oxide obtained via the acetate route.
Fig. 3. A typical IR spectrum of the nanocrystalline holmium oxides.
value of 10.608 Å as reported in Ref. [26] for the lattice parameter
of C-Ho is included in the ICDD-JCPDS PDF-2 powder diffraction
database [27].
3
. Results
2 3
O
3.1. Powder XRD patterns
3.2. IR spectra
X-ray diffraction pattern of powdered holmium oxide synthe-
sized from holmium chloride (Fig. 2, histogram 1) clearly exhibit
all Bragg reflections in the range of diffraction angles 20–70° which
are peculiar to the body-centered cubic (bcc) structure of holmium
IR spectra of the samples of holmium oxide are shown in Fig. 3.
The most intense absorption bands for the nanostructured oxides
ꢀ1
(
samples 1, 2 and 3) are at around 3430, 1500, 1400 and 850 cm .
oxide (the so-called holmiumsesquioxideHo
group Ia-3, with formula units per unit cell Z = 16). The XRD patterns
of the other oxides coincide with that of C-Ho only in the regions
2 3
O of the C-type, space
ꢀ1
Absorption bands at 1400 and 850 cm are due to the stretching
2
ꢀ
and out-of-plane bending vibrations of anions [CO
3
]
which are
2 3
O
bound to the RE metal ions on the surface of holmium oxide in a
of most intense peaks (Fig. 2 shows an XRD pattern from only the
sample 2). However, due to broadening, low-intense peaks become
indistinguishable against the noise. Furthermore, broad halos, char-
acteristic to X-ray amorphous substances, have not been observed in
the XRD patterns of the samples studied. Therefore we believe that
all the four samples were crystallized in the C-type crystal structure
ꢀ1
monodentate manner. An absorption band at 1500 cm can be
2
ꢀ
attributed to anions [CO
3
]
coordinated in a more complex manner
2
ꢀ
[
28]. Though the origin of ions [CO
3
]
may be different, they appear
onthesurfaceof holmiumoxide mostlybecauseof theefficientsorp-
tion of atmospheric carbon dioxide and water vapors in a process
CO + H O = H CO with the following reaction of the acid with the
2 2 2 3
2 3
of Ho O , and the crystallite sizes in the samples synthesized from
the organic precursors are small.
surface of the oxides [29].
It has also been shown [28] that the shape of IR spectra in the
The average crystallite size in the holmium oxide powder synthe-
sized from holmium chloride is thus seen (Table 2) to be much supe-
rior to those in the samples synthesized from the organic precursors.
Obviously, the method employed gives overestimated values of the
average crystallite size. Moreover, this method of the estimation of
the average crystallite size is known to be employed only when
the mean coherent scattering domain size is less then 100 nm (see,
for example, [25]). The resulting estimations, however, allow a con-
clusion that holmium chloride is not a suitable precursor for nano-
crystalline holmium oxide to be formed from the thermal
region related to the vibrations of CO
surface of La changes substantially depending on the concen-
tration of the adsorbed species. At high concentrations of CO even
a formation of La (CO can occur on the surface of the oxide. In
2
molecules adsorbed on the
2 3
O
2
2
3 3
)
the case of holmium oxides one cannot exclude this possibility be-
cause the IR spectra of the samples exhibit absorption bands sim-
ilar to those in the reported IR spectrum of La
2 3 3
(CO ) . Note that for
the well-crystallized holmium oxide the absorption bands assigned
2
ꢀ
to the vibrations of ions [CO
3
]
are relatively less intense, which
seems to be due to a smaller surface area of the sample.
decomposition of its salt. From here on we regard powdered Ho
synthesized from the chloride as a well-crystallized sample.
2 3
O
ꢀ1
A broad absorption band at 3430 cm is attributed to adsorbed
ꢀ1
water molecules and absorption bands at 2925 and 2855 cm — to
hydrocarbon impurities on the surface of holmium oxide.
It can also be seen from Fig. 2 that the interplanar spacings in
the nanocrystalline holmium oxide powder are larger than those
in the well-crystallized powder with bigger crystallite sizes. Table 2
presents the bcc lattice parameter, a, as calculated employing 4
Bragg reflections, for which the Miller indices are shown in
Fig. 2. It is obvious from the table that the lattice parameter de-
creases with increasing the crystallite size d. Note here, that a
3.3. Raman spectra
Raman spectra of the 4f metal oxides are rather complex and
depend on the exciting wavelength. The spectra can also include
Table 2
2 3
The average crystallite size d and the lattice parameter a for the studied samples of C-Ho O .
Sample number
222 Peak position (deg)
222 Peak FWHM (deg)
d (nm)
a (Å)
1
2
3
4
29.0436
29.0342
29.0376
29.1353
2.0162
1.6946
1.0948
0.112
8
10
16
10.6528 ± 0.0085
10.6471 ± 0.0063
10.6432 ± 0.0026
10.6073 ± 0.0005
4000

3
4
M.N. Abdusalyamova et al. / Journal of Alloys and Compounds 601 (2014) 31–37
5
% mass on heating up to 800 °C when the analysis is carried out
in argon or air, respectively. As mentioned in the Experimental
section, the sample 1 was prepared by the thermal decomposi-
tion of holmium acetate at 600 °C. However, following storage
of the sample under air is accompanied by adsorption of water,
carbon oxides and hydrocarbons, as evidenced by IR spectros-
copy. The adsorbed molecules and the products of their reaction
are at least partly responsible for the observed weight loss. Here a
question arises: what is the cause of the difference in the curves
of weight loss in argon and air? We believe that this discrepancy
is because the hydrocarbon contaminants formed during the
decomposition of the precursor are situated on the crystallite
boundaries of holmium oxide and gasify more effectively when
heated in air.
Thermal analysis data are consistent with the data of elemental
analysis which provides the following mass content of light ele-
ments in the sample of holmium oxide obtained from the acetate:
C — 1.1 ± 0.1; H — 0.43 ± 0.01; N — 0.3 ± 0.1; O — 4.7 ± 0.5. Here the
mass content of oxygen is attributed to the oxygen involved not in
the crystal lattice of holmium oxide powder, but in various species
adsorbed and chemisorbed on the powder surface. In total these
values give 6.5 ± 0.5 mass.%. That the total value somewhat ex-
ceeds that obtained by thermogravimetry (Fig. 5, green curve) is
because elemental analysis was carried out at a temperature more
than 1000 °C, whereas thermogravimetric analysis — only up to
Fig. 4. Comparison of the Raman spectra of well-crystallized (1) and nanostruc-
tured (2) Ho (Samples 4 and 2 in the Table 1, respectively).
2 3
O
signals associated with the photoluminescence from the metal ions
but not Raman scattering. It has been known [30] that the Raman
spectra of bcc RE O are expected to contain 22 peaks, while in
2 3
most experiments fewer are observed since some peaks overlap
or have relatively low intensity. The main (most intensive) Raman
is in the range of 320–420 cm–1 [31], with
2 3
O
peak of the oxides RE
there being a reliable relationship for the series of bcc RE
8
00 °C (Fig. 5, green curve).
2 3
O
oxides: the larger bcc crystal lattice parameter the smaller shift
of the main Raman peak it is [30].
3.5. Microstructural observations
In our case the position of the main Raman peak (375.1 cm–1,
Fig. 4) for the well-crystallized Ho
ment with the literature data (375 cm , see Table 1 in the Ref.
2 3
O (sample 4) is in a good agree-
TEM images of powder particles of holmium oxide synthesized
ꢀ1
via the acetate route (samples 1, 2) are shown in Fig. 6. The parti-
cles consist of disoriented domains having sizes of 10 nm, in
agreement with the XRD data discussed above. Electron diffrac-
tion patterns (Fig. 6b and d) indicate the presence of a certain tex-
ture, in agreement with lattice-resolution TEM observations
Fig. 6e).
In contrast to the case of samples 1 and 2, the preparation pro-
cedure of specimens for TEM does not allow an effective disrup-
tion of the majority of the aggregates of particles composing
holmium oxide powder obtained via the carbamide route at
[
32]). The Raman shift for the nanostructured holmium oxides
ꢀ1
(Fig. 4) is lower: 371.1–371.9 cm . Note here that the intensity
of Raman spectra for the samples 1, 2 and 3 in the main peak
region is more than an order of magnitude lower than that for
the sample 4. A similar effect (a decrease in the intensity of Raman
spectra with decreasing the mean coherent scattering domain size)
has also been observed earlier for nanostructured titanium diox-
ides [7,22,33–35].
The Raman spectrum of the nanostructured holmium oxide also
shows fewer pronounced peaks, the intensity of which is lower
than that of the main peak.
(
7
00 °C (sample 3) into components, the microstructure of which
would be visible in TEM. Under lower TEM magnification these
aggregates look like big single particles (Fig. 7a), non-transparent
for the electron beam. Only those aggregates are prone to ultra-
sonic disruption, which, as it turns out from TEM observations,
mainly contain particles typically looking like thin plates of a
uniform thickness (Fig. 7b). Electron diffraction patterns and
3.4. Thermal analysis
Fig. 5 displays weight change versus temperature for the sam-
ple 1 on heating in air and argon. There is a weight loss of 4% or
Fig. 5. Thermogravimetry and differential scanning calorimetry data for holmium oxide synthesized via the acetate route, as obtained on heating in air (curves 1) and argon
curves 2) flow.
(

M.N. Abdusalyamova et al. / Journal of Alloys and Compounds 601 (2014) 31–37
35
Fig. 6. TEM microstructure images and electron diffraction patterns of nanocrystalline holmium oxide obtained via the acetate route at 600 (a and b) and 700 °C (c–e).
lattice-resolution TEM images (Fig. 7c and d) show that the plates
are monocrystalline with low-angle (less than 1°) disorientation
over the full length of the plates. The sizes of monocrystalline
plates are substantially larger than the average crystallite size
measured by powder XRD for the sample 3. However, since TEM
and electron diffraction provide local information, these methods
can not characterize the sample 3 in whole. In contrast, powder
X-ray diffraction analysis method gives statistically averaged
information over a large volume of the sample 3 including the
aggregates of small particles mentioned above. It seems that
these aggregates contain particles with crystallites having aver-
age sizes close to those obtained from the broadening of the
X-ray diffraction (222) peak, i.e. 16 nm.
4. Discussion
We believe that the dependence of the crystallite size on the
nature of precursor is because the latter takes part in the properties
of crystallite boundaries, such as their strength. The stronger the
boundary the smaller the crystallite it is. Clearly, carbon atoms that
are needed to strengthen the boundaries may be present, for exam-
ple, as ions [CO3] , as pointed out above. However, the compari-
son of the samples obtained via the carbamide and acetate
routes shows that other elements also take part in the structure
of crystallite boundaries.
A transition from coarse, micro-sized crystallites to nano-sized
ones can be accompanied by changes in the interatomic distance in
the crystallites, even while the type of crystal lattice remains the
same. There have been a number of literature publications con-
firming this phenomenon. But the character of these changes can
be different. For instance, for metals, transition to nano-scale
dimensions usually results in a decrease in the interatomic
2
ꢀ
Holmium oxide powder obtained from holmium chloride (sam-
ple 4) substantially differs from the powders obtained from acetate
and carbamide with respect to the shape and structure of particles.
The particles of sample 4 are monocrystalline, round-shaped and
uniform in size 0.7–1 lm (Fig. 8).

3
6
M.N. Abdusalyamova et al. / Journal of Alloys and Compounds 601 (2014) 31–37
Fig. 7. TEM microstructure images of holmium oxide obtained via the carbamide route at 700 °C (a–c) and electron diffraction pattern corresponding to an extended thin
plate of the oxide (d).
Fig. 8. TEM image (a) and electron diffraction pattern and (b) of holmium oxide powders obtained from holmium chloride.
distance, i.e. the lattice contraction [36–40]. In some cases, how-
ever, the lattice expansion [41] or anomalous behavior [18] has
been observed. Under an assumption that nano-sized particles of
metals are spherical Qi et al. [16] have derived a simple equation
connecting the relative change in the crystal lattice parameter
(D
a/a) with the diameter of a particle d:
Da=a ¼ ꢀð1 þ k ꢁ dÞꢀ
1

M.N. Abdusalyamova et al. / Journal of Alloys and Compounds 601 (2014) 31–37
37
where the coefficient K is determined by the values of surface en-
ergy ( ) and rigidity modulus (G) of bulk materials: K = G/(2 ).
It is somewhat surprising that this simple equation satisfactorily
describes experimental data for the case of nano-sized palladium
particles [39].
[5] C.-H. Yan, Z.-G. Yan, Y.-P. Du, J. Shen, C. Zhang, W. Feng, Chapter 251.
Controlled synthesis and properties of rare earth nanomaterials, in: K.A.
Gschneidner, Jr., J.-C.G. Bünzli, V.K. Pecharsky (Eds.), Handbook on the Physics
and Chemistry of Rare Earths, Elsevier, 2011. pp. 275–472.
[6] A.A. Volodin, A.A. Belmesov, V.B. Murzin, P.V. Fursikov, A.D. Zolotarenko, B.P.
Tarasov, Inorg. Mater. 49 (2013) 656–662.
c
0
p
c
0
[
[
7] A.M. Molodets, A.A. Golyshev, Y.M. Shul’ga, Tech. Phys. 58 (2013) 1029–1033.
8] J. Virkutyte, S.R. Al-Abed, J. Nanopart. Res. 14 (2013).
In the case of binary metal oxides with nano-sized crystallites
there has been observed both the contraction (for instance, tita-
nium dioxide [42]), and the expansion (the present paper) of the
crystal lattice with decreasing the crystallite sizes. The expansion
is usually explained by the presence of interstitial impurities such
as hydrogen, carbon or oxygen (see, for example, Ref. [43]). Such
explanations, however, have often remained unproven, since to
identify the inclusions located inside the lattice represents a diffi-
cult task. In our case the presence of light atoms in the content of
holmium oxide powders obtained via the acetate and carbamide
routes is confirmed by elemental analysis. In addition, thermo-
gravimetry evidences that these impurities are retained on heating
up to 800 °C, which could be interpreted as a proof for the presence
[9] L. Eyring, The binary lanthanide oxides: synthesis and identification, in: G.
Meyer, L.R. Morss (Eds.), Synthesis of Lanthanide and Actinide Compounds,
Springer, Netherlands, 1991, pp. 187–224.
10] R.G. Haire, Chapter 125. Comparisons of the binary oxides, in: K.A.
Gschneidner, Jr., L. Eyring, G.H. Lander, G.R. Choppin (Eds.), Lanthanides/
Actinides: Chemistry, Elsevier Science B.V, 1994 (pp. 413–505).
11] V.B. Glushkova, A.G. Boganov, Russ. Chem. Bull. 14 (1965) 1101–1107.
12] E.L. Head, C.E. Holley Jr., The Preparation and Thermal Decomposition of the
Carbonates of Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc, Los Alamos Scientific Lab., N.
Mex, 1963.
13] E.L. Head, C.E. Holley Jr., in: L. Eyring (Ed.), Rare Earth Research, Gordon and
Breach, New York, 1965.
14] W.W. Wendlandt, Anal. Chem. 30 (1958) 58–61.
[15] W.W. Wendlandt, Anal. Chem. 31 (1959) 408–410.
16] W.H. Qi, M.P. Wang, Y.C. Su, J. Mater. Sci. Lett. 21 (2002) 877–878.
[
[
[
[
[
[
[
17] G.K. Rane, U. Welzel, S.R. Meka, E.J. Mittemeijer, Acta Mater. 61 (2013) 4524–
2 3
of interstitials inside the crystal lattice of C-Ho O .
4533.
Thus, to determine a priori the dependence of the lattice param-
eter on the crystallite size for complex structures is not possible so
far. Therefore, reliable experimental works in this direction are still
urgent.
[18] J. Sheng, G. Rane, U. Welzel, E.J. Mittemeijer, Physica E. 43 (2011) 1155–1161.
[
[
[
19] H. Wang, J. Huang, L. Zhang, J. Li, Mater. Chem. Phys. 141 (2013) 101–106.
20] L. Yang, L. Li, M. Zhao, C. Fu, G. Li, Nanotechnology 24 (2013) 305701.
21] C. Solliard, M. Flueli, Surf. Sci. 156 (1985) 487–494.
[22] Y.M. Shul’ga, D.V. Matyushenko, E.N. Kabachkov, A.M. Kolesnikova, E.N.
Kurkin, I.A. Domashnev, et al., Tech. Phys. 55 (2010) 141–143.
[
[
23] J.B. Kortright, A.C. Thompson, Section 1.2 X-Ray emission energies, in: A.C.
Thompson (Ed.), X-ray Data Booklet, third ed., Lawrence Berkeley National
Laboratory, University of California, Berkeley, CA, 2009 (pp. 1–8 to 1–27).
24] R.D. Deslattes, E.G. Kessler, P. Indelicato, L. de Billy, E. Lindroth, J. Anton, X-ray
transition energies: new approach to a comprehensive evaluation, Rev. Mod.
Phys. 75 (2003) 35–99.
5
. Conclusions
1
2 3
. Powders of holmium oxide C-Ho O were synthesized with the
use of different precursors, such as holmium chloride, holmium
acetate, and carbamide-containing complex of holmium.
. The mean coherent scattering domain size in the crystal phase
of holmium oxide formed on heating at 600 and 700 °C depends
on the nature of precursors and averages 10 nm in the case of
the organic ones.
. The data of XRD analysis and Raman spectroscopy consistently
indicate that the bcc lattice parameter of nanocrystalline pow-
ders of holmium oxide exceeds that for the well-crystallized
powder.
[25] B.D. Cullity, Elements of X-Ray Diffraction, second ed., Addison Wesley
Publishing Company, 1978.
[
2
26] B. Antic, M. Mitric, D. Rodic, Structure properties and magnetic susceptibility
x 3
of diluted magnetic semiconductor Y2ꢀxHo O , J. Magn. Magn. Mater. 145
(1995) 349–356.
27] ICSD: Home, <http://www.fiz-karlsruhe.de/icsd.html>.
28] O.V. Manoilova, S.G. Podkolzin, B. Tope, J. Lercher, E.E. Stangland, J.-M. Goupil,
et al., J. Phys. Chem. B 108 (2004) 15770–15781.
[
[
3
4
[29] D. Bloor, J.R. Dean, J. Phys. C: Solid State 5 (1972) 1237–1252.
[
30] Y. Repelin, C. Proust, E. Husson, J.M. Honig, J. Solid State Chem. 118 (1995)
63–169.
31] A. Ubaldini, M.M. Carnasciali, J. Alloys Comp. 454 (2008) 374–378.
1
[
. Main impurities in the nanocrystalline powders of holmium
oxide are carbonate ions and water.
[32] N. Dilawar, S. Mehrotra, D. Varandani, B.V. Kumaraswamy, S.K. Haldar, A.K.
Bandyopadhyay, Mater. Charact. 59 (2008) 462–467.
[
[
33] W. Ma, Z. Lu, M. Zhang, Appl. Phys. A 66 (1998) 621–627.
34] Y.M. Shul’ga, E.N. Kabachkov, D.V. Matyushenko, E.N. Kurkin, I.A. Domashnev,
Tech. Phys. 56 (2011) 97–101.
Acknowledgements
[35] Y.M. Shul’ga, D.V. Matyushenko, A.A. Golyshev, D.V. Shakhrai, A.M. Molodets,
E.N. Kabachkov, et al., Tech. Phys. Lett. 36 (2010) 841–843.
[
[
36] J.S. Vermaak, C.W. Mays, D. Kuhlmann-Wilsdorf, Surf. Sci. 12 (1968) 128–133.
37] C.W. Mays, J.S. Vermaak, D. Kuhlmann-Wilsdorf, Surf. Sci. 12 (1968) 134–140.
The work was performed under the financial support of Interna-
tional Science and Technology Center (Project No T-1882).
[38] P.A. Montano, W. Schulze, B. Tesche, G.K. Shenoy, T.I. Morrison, Phys. Rev. B. 30
1984) 672–677.
(
[
[
39] R. Lamber, S. Wetjen, N.I. Jaeger, Phys. Rev. B 51 (1995) 10968–10971.
40] J.T. Miller, A.J. Kropf, Y. Zha, J.R. Regalbuto, L. Delannoy, C. Louis, et al., J. Catal.
References
2
40 (2006) 222–234.
[
1] G.S. Brady, H.R. Clauser, J.A. Vaccari, Materials Handbook, fifteenth ed.,
McGraw-Hill, New York, 2002.
[41] Z. Wei, T. Xia, J. Ma, W. Feng, J. Dai, Q. Wang, et al., Mater. Charact. 58 (2007)
1019–1024.
[
[
2] G.A.H. Mekhemer, Appl. Catal. A: Gen. 275 (2004) 1–7.
3] K.P. Jayadevan, T.Y. Tseng, Oxide nanoparticles, in: H.S. Nalwa (Ed.),
Encyclopedia of Nanoscience and Nanotechnology, American Scientific
Publishers, Stevenson Ranch, Calif, 2004, pp. 333–376.
[42] K. Madhusudan Reddy, S.V. Manorama, A. Ramachandra Reddy, Mater. Chem.
Phys. 78 (2003) 239–245.
[43] C. Kuhrt, R. Anton, Thin Solid Films 198 (1991) 301–315.
[44] G.H. Zschornack, Handbook of X-Ray Data, Springer, Berlin Heidelberg, 2007.
[
4] N. Imanaka, T. Masui, Particles and single crystals of rare earth oxides, in: G.
Adachi, N. Imanaka, Z. Kang (Eds.), Binary Rare Earth Oxides, Springer,
Netherlands, 2005, pp. 135–161.