Evidence for phase transitions and pseudospin phonon coupling in K-0.9(NH4)(0.1)H2AsO4

Kumar, Pradeep and Ramesh, KP and Muthu, DVS (2015) Evidence for phase transitions and pseudospin phonon coupling in K-0.9(NH4)(0.1)H2AsO4. In: AIP ADVANCES, 5 (3).

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Abstract

This work reports a detailed temperature dependent Raman study on the mixed crystals of K-0.9(NH4)(0.1)H2AsO4 (KADA) from 5K to 300K in the spectral range of 60-1200cm(-1), covering tetragonal to orthorhombic structural phase transition accompanied by paraelectric to ferroelectric transition at T-c* similar to 60K. Multiple phase transitions below transition temperature (Tc* similar to 60K) are marked by the appearance of new modes, splitting of existing ones as well as anomalies in the self-energy parameters (i.e. mode frequencies and damping coefficient) of the phonon modes. Temperature independent behaviour of damping coefficient and abrupt jump in the mode frequency of some of the internal vibrations of AsO4 tetrahedra as well as external vibrations clearly signal long range ferroelectric ordering and proton ordering below T-c*. In addition, we observed that temperature dependence of many prominent phonon modes diverges significantly from their normal anharmonic behaviour below T-c* suggesting potential coupling between pseudospins and phonons. (C) 2015 Author(s).

Item Type:	Journal Article
Publication:	AIP ADVANCES
Publisher:	AMER INST PHYSICS
Additional Information:	Copy right for this article belongs to the AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Keywords:	RAMAN-SCATTERING; OPTICAL PHONONS; FERROELECTRICS; CRYSTALS; BEHAVIOR
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	06 May 2015 05:17
Last Modified:	06 May 2015 05:17
URI:	http://eprints.iisc.ac.in/id/eprint/51490

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