Growth from the Melt and Properties Investigation of ScF3 Single Crystals

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.

Integrating Abnormal Thermal Expansion and Ultralow Thermal Conductivity into (Cd,Ni)2re2o7 Via Synergy of Local Structure Distortion and Soft Acoustic Phonons

“…2b presents electrical conductivity (σ) versus thermal conductivity of various material types. CRO and CRON5 with ultralow κ stand out again, showing decent electrical conduction (15.1 and 16.1 S/cm at 300 K, respectively), several orders of magnitude higher than that of representative NTE insulators whose σ is inclined below 10 -6 S/cm [25], such as ZrW 2 O 8 , Zn 4 B 6 O 13, and ScF 3 . Moreover, this magnitude of σ is comparable with common semiconductors, like GaAs and Ge.…”

“…[23] In terms of prototypical NTE materials with low thermal conductivity, they demonstrate so inferior electrical conductivities (as low as 10 -6 S/cm) that they are incapable of effective electrical conduction. [24,25] As regard NTE alloys, their high electrical conductivities are prone to result in unexpectedly overhigh thermal conductivity, disabling to resist thermal shock. To date, such seemingly intrinsic contradictions, as a consequence, lead to no report about excellent integration of abnormal thermal expansion and ultralow thermal conductivity into single-phase materials with decent electrical conduction.…”

Low‐temperature phase formation in the SrF2–LaF3 system

“…The composition of Sr 0.7 La 0.3 F 2.3 with a melting point of 1570°C is the most refractory inorganic fluoride, surpassing scandium fluoride ScF 3 with the melting point of 1550°C. 8,9 Melting temperature of SrF 2 is 1464°C, 4 and melting point of LaF 3 is 1500°C. 4,8 The maxima on the melting curves of solid solutions correspond to the congruent type of melting, which makes the corresponding compositions promising for growing single crystals of high optical quality from the melt, since it excludes the possibility of concentration undercooling and, formation of inhomogeneities of the cellular substructure type respectively.…”

“…The formation of maxima indicates the stabilization of crystal structures by isomorphic substitutions. The composition of Sr 0.7 La 0.3 F 2.3 with a melting point of 1570°C is the most refractory inorganic fluoride, surpassing scandium fluoride ScF 3 with the melting point of 1550°C 8,9 . Melting temperature of SrF 2 is 1464°C, 4 and melting point of LaF 3 is 1500°C 4,8 …”

Low-temperature luminescence of ScF3 single crystals under excitation by VUV synchrotron radiation

“…Scandium fluoride (ScF 3 ) is a wide-bandgap material belonging to perovskite-type compounds [1]. ScF 3 demonstrates strong negative thermal expansion (NTE) [2], which is more pronounced than that of most known NTE materials.…”