Growth from the Melt and Properties Investigation of ScF3 Single Crystals

Denis Karimov,Irina Buchinskaya,Nikolay Sorokin,Pavel Prosekov,Tatiana Glushkova,Vadim Grebenev,Pavel Popov,Natalia Arkharova

doi:10.3390/cryst9070371

Abstract

ScF3 optical quality bulk crystals of the ReO3 structure type (space group P m 3 ¯ m , a = 4.01401(3) Å) have been grown from the melt by Bridgman technique, in fluorinating atmosphere for the first time. Aiming to substantially reduce vaporization losses during the growth process graphite crucibles were designed. The crystal quality, optical, mechanical, thermal and electrophysical properties were studied. Novel ScF3 crystals refer to the low-refractive-index (nD = 1.400(1)) optical materials with high transparency in the visible and IR spectral region up to 8.7 µm. The Vickers hardness of ScF3 (HV ~ 2.6 GPa) is substantially higher than that of CaF2 and LaF3 crystals. ScF3 crystals possess unique high thermal conductivity (k = 9.6 Wm−1К−1 at 300 K) and low ionic conductivity (σ = 4 × 10−8 Scm−1 at 673 К) cause to the structural defects in the fluorine sublattice.

Highlights

Crystalline materials based on the rare-earth fluorides RF3 play a significant role in the photonics and optoelectronic instrument engineering for many years [1]
In the RF3 row, it is the only one that has structural ReO3 type and it belongs to the perovskite-like compounds family with the common formula ABХ3, in which the position of one of the cations is vacant
In the ScF3 structure, Sc3+ cations are located at the vertices of the primitive cubic cell

Summary

Introduction

The stability of the RF3 structural type under standard conditions changes in the rare-earth row as R3+. Ionic radius decreases [1]: LaF3 -type (tysonite) → β-YF3 (Fe3 C-cementite) → ReO3. In this case coordination number (CN) of the rare-earth cations changes, respectively, from CN = 11 (LaF3 -type) to CN = 8–9 (β-YF3 -type), and up to CN = 6 (ReO3 -type). In the RF3 row, it is the only one that has structural ReO3 type and it belongs to the perovskite-like compounds family with the common formula ABХ3 , in which the position of one of the cations (at the unit cell center) is vacant. Volume voids in the structure give place to its looseness

Objectives

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Results

Conclusion