Structural Transformation in Inverse-Perovskite REPt₃B (RE = Sm and Gd–Tm) Associated with Large Volume Reduction

Abstract

In this work, we report the structural phase transformation of tetragonal inverse-perovskite REPtB (RE = Sm, and Gd-Tm) compounds to cubic perovskite structure, with a large volume reduction of about 9% (reduction of the c axis, ∼17%; increase in the a axis, ∼5%). The structural stability of the cubic phase, however, could only be maintained by lowering the lattice parameter of the off-stoichiometric REPtB (x < 1), formed in the process of annealing. The combined effect of phase transformation and stoichiometric defects is argued to be responsible for the observed volume collapse. Unexpectedly, the application of a large hydrostatic pressure of ∼20 GPa does not have any significant effect on the crystal structure. Neutron diffraction studies and heat capacity measurements unambiguously confirm different magnetic transition temperatures in the tetragonal and cubic phases. The different physical properties of these two phases demonstrate the interrelationship between the crystal chemistry and the physics of the system. The synthetic route to cubic REPtB identified in this work may be utilized to prepare new ternary rare-earth intermetallics in a cubic perovksite form, which was previously found to facilitate unconventional superconductivity.

Physical properties of RIr3 (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases

“…The RIr 3 system thus form as a macroscopic coexistence of two crystalline phases, cubic C15b and cubic AuCu 3 -type with different relative percentage for different rare earths (Table I). Coexistence of similar polymorphic phases have earlier been reported in literature 11,22 . For example it is recently reported that RPt 3 B compounds form in two polymorphic crystal structures, tetragonal CePt 3 B-type and and ideal cubic perovskite-type at room temperature 11 .…”

“…To check the homogeneity of the materials, EDX measurement have been carried out which confirms that the RIr 3 compounds are chemically homogeneous with rare earth and transition metal ratio 1:3. It therefore appears to be quite likely that these compounds form in new crystal structure or the extra peaks may come from coexisting additional polymorphic phase similar to that reported earlier in RPt 3 B series of compounds 11 . It may also be pointed out here that binary TbPt 3 compounds are also known to form in two different polymorphic phases TbPt 3 : C15b and AuCu 3 -type 12 .…”

“…Therefore, to study the effect of polymorphism on physical properties, it is highly desirable to obtain different phases under similar environment, viz., temperature, pressure, etc. Similar to RIr 2 Si 2 series of compounds, it has been recently shown that RPt 3 B-type (R = rare earth) of compounds that form in tetragonal crystal structure, changes to cubic perovskite like structure when annealed at high temperature 11 , although the structural change found to be associated with creation of partial vacancy in the body-center position. One may note here that the different members of binary RPt 3 (R = rare earth) compounds are known to form in two different crystal structures: C15b type for R = La-Tb, and AuCu 3 -type for R = Dy-Lu [12][13][14][15] .…”

Insight into various properties of rare‐earth–based inverse perovskites Gd 3 AlX (X = B, N)

“…Recently, they are emerging as potential applicants for topological insulators and three‐dimensional Dirac electron systems . A series of rare‐earth–based inverse perovskites have been studied for various properties to find vital application in various fields . Several inverse perovskites have been prepared, characterized, and studied like A 3 NIn, A 3 NSn, and A 3 XAl, where (A = Sc, La, Ce, Pr, Nd, Sm, Gd‐Tm, Lu) and (X = C, N, O).…”

“…17 A series of rare-earth-based inverse perovskites have been studied for various properties to find vital application in various fields. [18][19][20][21][22][23] Several inverse perovskites have been prepared, characterized, and studied 24,25 like A 3 NIn, A 3 NSn, and A 3 XAl, where (A = Sc, La, Ce, Pr, Nd, Sm, Gd-Tm, Lu) and (X = C, N, O). The electronic and magnetism properties of Gd 3 AlX (X = B, N) were investigated by Kacimi et al 26 We have further extended the investigation on these materials for elastic, thermodynamic, thermoelectric, and optical properties for various applications.…”