Synthesis, structure and optical properties of EuF3 film-forming material

Article abstract of DOI:10.1016/S0925-8388(02)00779-X

The crystal structure of europium trifluoride, α-EuF₃, synthesized by consecutive dissolving was refined. The optical and operational properties of thin film coatings prepared from this material using thermal evaporation were studied. The coati

Full text of DOI:10.1016/S0925-8388(02)00779-X

Journal of Alloys and Compounds 347 (2002) L1–L3
L
www.elsevier.com/locate/jallcom
Letter
Synthesis, structure and optical properties of EuF3 film-forming material
b
V.F. Zinchenkoa, N.P. Efryushinaa, O.G. Eryomina, V.Ya. Markivb , , N.M. Belyavina ,
*
O.V. Mozkovac, M.I. Zakharenkob
aA.V.Bogatsky Physico–Chemical Institute NASU, 86, Lyustdorfska Doroga Street, 65080, Odesa, Ukraine
bTaras Shevchenko Kyiv National University, 64, Volodymyrska Street, 01003, Kyiv, Ukraine
cArsenal Central Design Office, 8, Moscovska Street, 02010, Kyiv, Ukraine
Received 26 September 2001; received in revised form 9 April 2002; accepted 9 April 2002
Abstract
The crystal structure of europium trifluoride, a-EuF3, synthesized by consecutive dissolving was refined. The optical and operational
properties of thin film coatings prepared from this material using thermal evaporation were studied. The coatings were shown to contain
either single b-EuF3 or an a-EuF3 and b-EuF3 mixture, depending on the preparation conditions.
2002 Elsevier Science B.V. All rights reserved.
Keywords: Rare earth compounds; Crystal structure; Optical properties
t
1. Introduction
2EuCl3 1 3H2F2 →2EuF3↓ 1 6HCl
(2)
The crystallographic data [1] and thermodynamic
characteristics [2] of europium trifluoride EuF3 were
studied. It was found, in particular, that EuF3 crystallizes
in two polymorphic modifications, namely: high-tempera-
ture b-EuF3 and low-temperature a-EuF3 forms. Accord-
ing to the data of Greis [1] the crystal structure of b-EuF3
Then the precipitate was carefully washed and dried
under melted alkali in vacuum (for terminal removal of the
water and acid). After that it was aged in vacuum at 500 8C
for 15–20 min. A portion of the product was melted in a
graphite crucible in an inert (argon) atmosphere, and
another portion was sintered as a pellet at 1000 8C. The
melted specimen was white with a yellow tint, and the
sintered one was a pure white color.
The obtained materials were tested using the X-ray
phase and structure analysis. The diffraction data were
collected with an automated Dron-3 diffractometer in a
discrete regime [step scan (0.02–0.05)8, counting time per
step (4–8) s] using filtered copper radiation. The prelimin-
ary treatment of the diffraction pattern was carried out by a
full profile analysis. The phase analysis and the structure
calculations were carried out using a hardware/software
device, as reported in [3].
Thin film coatings of the europium trifluoride were
deposited on different substrates (K8 optical glass, ger-
manium, silicon, etc.) heated up to 200 8C by evaporation
of the prepared pellets in a VU–1A vacuum supply under a
residual pressure of (2–3)?10–3 Pa. The evaporation was
performed either under the action of an electron beam or
by resistive heating from molybdenum boats. The optical
thickness of the coatings (nd) was varied from 0.8 to 2.4
mm. The refraction index (n), the scattering index (s) and
¯
belongs to the tysonite structure type (P3c1 space group;
˚
˚
a56.9204 A, c57.0856 A) and a-EuF3 to the YF3-low
˚
structure type (anti-Fe3C) (Pnma; a56.6105 A, b57.0157
˚
˚
A, c54.3959 A). It should be emphasized that no data on
the crystal structure refinement for both polymorphic
modifications were reported before.
2. Experimental
The specimens of europium trifluoride were synthesized
by consecutive dissolving of high-purity europium oxide
(99.9 wt.% purity) in hydrochloric acid with a subsequent
EuF3 precipitation using concentrated H2F2 according to
the reactions:
Eu2O3 1 6HCl → 2EuCl3 1 3H2O
(1)
*
Corresponding author.
E-mail address: belmar@univ.kiev.ua (V.Ya. Markiv).
0925-8388/02/$ – see front matter
PII: S0925-8388(02)00779-X
2002 Elsevier Science B.V. All rights reserved.

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V.F. Zinchenko et al. / Journal of Alloys and Compounds 347 (2002) L1–L3
Table 1
Crystallographic data for a-EuF3 in a sintered sample
Atom
Site
x
y
z
Eu
F(1)
F(2)
4c
4c
8f
0.365(1)
0.522(2)
0.171(2)
0.25
0.25
0.065(2)
0.063(1)
0.576(6)
0.393(4)
Space group
Pnma (no. 62)
dcal 56.92
84
Calculated density (g cm23
Independent reflections
)
2
˚
Isotropic temperature factor (A )
B520.1(2)
Texture parameters
t50.90(2), texture axis [010]
Reliability factor
RW 50.051
mechanical durability of the deposited coatings have been
determined.
The diffraction patterns of the coatings deposited by
resistive evaporation differ essentially from those of the
source material. These patterns could be indexed in a
˚
˚
hexagonal lattice with a56.91(1) A, c57.08(1) A.
Reasoning from the data of Ref. [1] on the existence of a
high-temperature modification of EuF3 we chose the
3. Results and discussion
¯
The data of the X-ray diffraction (XRD) study proved
that the heat-treated sintered (of white color) and the
melted (of white color with the yellow tint) samples of the
EuF3 products were single-phased. Their diffraction pat-
terns were indexed in an orthorhombic lattice with a5
tysonite type structure (P3c1 space group) as the starting
model to calculate the EuF3 structure in the coatings.
Taking into account the complex texture distribution in the
studied coatings ([001] texture axis slightly deviates from
the surface normal, i.e. the texture is dispersed) the
reliability factor was successfully reduced to RW 50.25
due to the refinement of the positional and temperature
parameters. Further attempts to improve the RW value
failed. The diffraction patterns of the coatings deposited by
electron beam evaporation showed that the coatings con-
tain a mixture of a-EuF3 and b-EuF3.
˚
˚
˚
6.616(1) A, b57.013(4) A, c54.392(2) A and a5
˚
˚
˚
6.620(1) A, b57.016(1) A, c54.392(2) A, respectively.
Full structure calculations of the diffraction patterns for
both probes, which differed in the gradations of the white
color, was carried out to check whether they belong to the
anti-Fe3C-type structure.
The calculation of the diffraction pattern of the sintered
sample confirms that its a-EuF3 crystal structure belongs
to the anti-Fe3C-type structure. The values of the position-
al and temperature parameters of this trial structure have
been refined within the structure model in which europium
and fluorine atoms completely occupy the 4c and 8f sites
of the Pnma space group, respectively (Table 1).
A similar calculation of the diffraction pattern of the
melted sample using the distribution of atoms according to
the model used for the a-EuF3 structure in a sintered
sample (with accounting of texture) resulted in a value of
the reliability factor of about 0.10 after the refinement of
the positional parameters. Further attempts to decrease the
value of the reliability factor within the anti-Fe3C structure
type model failed.
The values of optical and operational parameters of the
coatings (Table 2) display some dependence on the nature
of material and on the mode of evaporation. The refraction
index of the coatings range from 1.5 to 1.6. The scattering
index is equal to (0.03–0.12)% and has the lowest value
for a coating deposited by resistive evaporation of the
sintered a-EuF3. Just this coating possesses the best
operational characteristics, especially mechanical durabili-
ty.
4. Conclusions
It was shown that during the synthesis of europium
trifluoride performed under different thermal conditions
Table 2
Optical and operational characteristics of the EuF3-based thin film coatings
Mode of syntheses
Deposited coat
Phase
composition
Mode of
deposition
Phase
composition
na
s
Mechanical
durabilityb
(%)
Sintered at 1000 8C
Melted in a graphite crucible
Sintered at 1000 8C
a-EuF3
a-EuF3
a-EuF3
Resistive
Resistive
Electron-beam
b-EuF3
b-EuF3
b-EuF3 1a-EuF3
1.60–1.61
1.56
1.52–1.56
0.03–0.04
0.06–0.08
0.11–0.12
17 000 rot.
5000 rot.
1000 rot.
a The refraction index of the films has been calculated using the data of the spectral measurements in 0.5–2.0 mm region.
b The mechanical durability was estimated by the number of rotation periods that the coat withstand rubbing while testing at SM-55 device.

V.F. Zinchenko et al. / Journal of Alloys and Compounds 347 (2002) L1–L3
L3
(sintering or melting) it crystallized in the a-EuF3 poly-
References
morphic form. Thin-film coatings deposited by thermal
evaporation or electron beam evaporation contain mainly
the high-temperature b-EuF3 phase. Some optical and
operational properties of these thin film coatings were
studied. The coatings prepared by resistive evaporation of
the sintered a-EuF3 were shown to possess the best
operational characteristics.
[1] O. Greis. Private communication, (1976). Cyt. by The Powder
Diffraction File (PDF-2) (1993).
[2] N.P. Galkin, Ya.N. Tumanov, Yu.P. Butylkin, Thermodynamical
Properties of Inorganic Fluorides. Handbook, Atomizdat, Moscow,
1972.
[3] V.Ya. Markiv, N.M. Belyavina, in: Proceeding of the Second
International Scientific Conference of Engineering and Functional
Materials, EFM-97, L’viv, 14–16 October, 1997.
Acknowledgements
This work was supported by the Science and Technolo-
gy Center in the Ukraine (STCU) (Project No. 1356).