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ABSTRACT: Using optical spectroscopy and complex impedance measurements, we have studied the transmission spectra and electrical conductivity
of different BaF2 samples: ceramic prepared by vacuum hot pressing (200 MPa, 870°C, 20 min), the same ceramic after heat treatment in a reactive
HF atmosphere (1200°C, 120 min), and a single crystal grown from the melt in vacuum. Heat treatment of the as-prepared BaF2 ceramic in a fluorination atmosphere increases its optical transmission in the range 0.2–0.8 µm on average by a factor of
2 and markedly reduces the selective absorption in the range 6–11 µm. The heat-treated BaF2 ceramic is close in ionic conductivity to the BaF2 single crystal.
Inorganic Materials 05/2012; 45(10):1188-1192. · 0.41 Impact Factor
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ABSTRACT: Homogeneous crystals of Ca0.59Sr0.41F2 alloy (sp. gr., Fm
$
\bar 3
$
\bar 3
m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF2-SrF2 phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties
of Ca0.59Sr0.41F2 and MF2 crystals (M = Ca, Sr) have been studied and comparatively analyzed. Ca0.59Sr0.41F2 crystals are transparent in the range of 0.133–11.5 μm, have refractive index n
D
= 1.436, microhardness H
μ = 2.63 ± 0.10 GPa, ion conductivity σ = 5 × 10−5 S/cm at 825 K, and thermal conductivity k = 4.0 W m−1 K−1 at 300 K. It is shown that the optical properties of Ca0.59Sr0.41F2 crystals are intermediate between those of CaF2 and SrF2, whereas their mechanical and electrical characteristics are better than the latter compounds.
Crystallography Reports 04/2012; 55(3):518-524. · 0.47 Impact Factor
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ABSTRACT: Single crystals of the Ca1 − x
Sc
x
F2 + x
(x = 0.106, 0.132, 0.156) solid solutions (CaF2 structure type, space group Fm
$
\bar 3
$
\bar 3
m) are investigated using X-ray diffraction. It is revealed that the crystals under investigation contain vacancies in the
8c positions and interstitial fluorine ions in the 48i positions. The coordination number of Sc3+ ions in the structure of the Ca1 −x
Sc
x
F2 + x
solid solutions is equal to eight. The specific features of the concentration dependences of the ionic conductivity and the
activation energy of ion transfer for the Ca1 − x
Sc
x
F2 + x
(0.02 ≤ x ≤ 0.15) solid solutions are explained in the framework of the percolation model of conducting “defect regions.” The percolation
threshold equal to 3–5 mol % ScF3 corresponds to the model of [Ca14 − n
Sc
n
F68] octacubic clusters containing fluorine ions in the 48i positions. The ionic conductivity of the Ca1 − x
Sc
x
F2 + x
solid solutions is analyzed in comparison with the change in this characteristic for the series of Ca0.8
R
0.2F2.2 crystals with rare-earth elements.
Crystallography Reports 04/2012; 54(4):572-583. · 0.47 Impact Factor
