Structural Phase Transitions in Rb2KMIIIF6 Elpasolites. I. Crystal Chemistry and Calorimetric Studies

Abstract

Structural phase transitions are characterized in several elpasolites corresponding to the general formula Rb2KMIIIF6 (M = Al, Cr, Fe, Y, Bi) using X‐ray diffraction and calorimetric techniques. The increase of the transition temperature with increasing M3+ size — as observed for most terms of the series — can be related to simultaneous decrease of the Goldschmidt tolerance factor t towards the lower limit of the stability range of the cubic lattice. Evidence is given of the symmetries of the high‐ and low‐temperature forms, together with preliminary transition entropies. Large single crystals of Rb2KFeF6 and Rb2KYF6 are grown using a Bridgman method.

ESR Investigation of Phase Transitions in Some Elpasolite‐Type Fluorides

“…In the case of Rb,KFeF, an important jump ( 3 5 0~1 0 -~T ) occurs around 170K corresponding to the structural phase transition, as observed by XRD [2]. An additional weaker increase of the linewidth (100 x T) is noticed around 110 K (Fig.…”

“…As the temperature is lowered the compound undergoes a structural phase transition and becomes tetragonal due to low value o f t as previously observed in other elpasolites [2]. The tetragonal unit cell constants (14/rnmm-derived space group) are related to the cubic parameter by: stet, x aoub/l/2; ctetr w acub.…”

Highly stable, phase pure Cs2AgBiBr6 double perovskite thin films for optoelectronic applications

“…19 Bismuth-containing elpasolites with A = Rb, Cs, CH3NH3; M 1+ = Na, K, Tl and X = F, Cl, Br have been investigated for several decades. [20][21][22][23][24] Unfortunately, compounds containing alkali metals do not absorb light in the visible range due to their large band gap energies (Eg) exceeding 3 eV. 20,25 Although the thallium-containing compound features a reasonable small Eg of 2.16 eV, the severe toxicity of thallium excludes this element as a non-toxic alternative for lead.…”

Toward Lead-Free Perovskite Solar Cells

“…A more recent review suggests that at least 350 different elpasolites have been synthesized . In Figure we highlight all the elements of the periodic table which belong to known halide elpasolites. ,− A simple count indicates that 7 elements are found as A-site cations, 8 elements can occupy the B + sites (including ammonium and methylammonium), 34 elements are found as B 3+ cations, and 5 elements can occupy the X sites (including the cyanide CN – ). A straightforward multiplication of these numbers yields a stunning 9520 combinations.…”