Dion–Jacobson(<i>n</i> = 2) LayeredPerovskites (A′SmTa₂O₇; A′ = Rb,Cs) As Potential Ferroelectric Materials

The search for new polar materials with switchable polarization is being explored with vigorous experimental efforts combined with theoretical tools. Particularly, several members of the Dion–Jacobson (DJ) family of layered perovskites have been identified in noncentrosymmetric (NCS) polar structures toward potential ferroelectric materials. The polarity attributed to the mechanism of hybrid-improper ferroelectricity has opened up a flurry of activity to reexamine the structures and properties of the various layered perovskite oxides. We present here the systematic studies on the crystal structures and phase transitions of the <i>n</i> = 2 DJ oxides, RbSmTa₂O₇ (S. G. <i>I</i>2<i>cm</i>, <i>a</i> = 5.4177(8) Å, <i>b</i> = 5.3906(9) Å, <i>c</i> = 22.0952(3) Å) and CsSmTa₂O₇ (S. G. <i>P</i>2₁<i>am</i>, <i>a</i> = 5.4421(5) Å, <i>b</i> = 5.4136(5) Å, <i>c</i> = 11.2493(1) Å) crystallizing in NCS space groups authenticated through structural refinements by the Rietveld method. Room temperature Raman spectral measurements confirm the symmetry lowering in the polar structure along with polarization switching experiments. Structural phase transitions from polar (S. G. <i>I</i>2<i>cm</i>) to nonpolar (S. G. <i>P</i>4/<i>mmm</i>) structures for RbSmTa₂O₇ occurring around 1075 K and for CsSmTa₂O₇ (from S. G. <i>P</i>2₁<i>am</i> to <i>P</i>4/<i>mmm</i>) occurring around 710 K are corroborated through variable temperature dielectric measurements.