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Structural phase transitions drive several unconventional phenomena includingsome illustrious ferroic attributes which are relevant for technologicaladvancements. With this note, we have investigated the structural transition ofperovskite-type trigonal Ba2ZnTeO6, across Tc ~ 150 K, which is alsoaccompanied by a para- to ferroelastic transition. With the help of Ramanspectroscopy and density-functional theory (DFT)-based calculations, here wereport new intriguing observations associated with the phase transition inBa2ZnTeO6 elucidating the lattice dynamics across the Tc. We have observed thepresence of a central peak (quasi-elastic Rayleigh profile), huge softening inthe soft mode, hysteretic phonon behavior, and signatures of coexistent phases.The existence of a central peak in Ba2ZnTeO6 is manifested by a sharp rise inthe intensity of the Rayleigh profile in concomitant with the damping of thesoft mode near Tc, shedding light on the lattice dynamics during the phasetransition. While most of the phonon bands split below Tc confirming the phasetransition, we have observed thermal hysteretic behavior of phonon modes thatsignifies the first-order nature of the transition and presence of coexistingphases, which are corroborated by our temperature-dependent x-ray diffractionand specific heat measurements. Further, an evidence of the concomitantstructural transition appears in the form of huge softening in the thermalresponse of the soft phonon mode at ~ 31 cm-1 which is remarkable compared tothe hitherto known behavior of soft modes in well-known ferroelectrics. This isfurther corroborated by our phonon calculations that show an unstable Eg-modein the high-symmetry structure involving TeO6 octahedral rotation (with Ba andZn translation) which later condenses into the C2/m low-symmetry phase.

Lattice dynamics across the ferroelastic phase transition in Ba2ZnTeO6: A Raman and first-principles study