skip to main content

Title: Evidence for phase transitions and pseudospin phonon coupling in K{sub 0.9}(NH{sub 4}){sub 0.1}H{sub 2}AsO{sub 4}

This work reports a detailed temperature dependent Raman study on the mixed crystals of K{sub 0.9}(NH{sub 4}){sub 0.1}H{sub 2}AsO{sub 4} (KADA) from 5K to 300K in the spectral range of 60-1200cm{sup −1}, covering tetragonal to orthorhombic structural phase transition accompanied by paraelectric to ferroelectric transition at T{sub c}{sup *} ∼ 60K. Multiple phase transitions below transition temperature (T{sub c}{sup *} ∼ 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 AsO{sub 4} tetrahedra as well as external vibrations clearly signal long range ferroelectric ordering and proton ordering below T{sub c}{sup *}. In addition, we observed that temperature dependence of many prominent phonon modes diverges significantly from their normal anharmonic behaviour below T{sub c}{sup *} suggesting potential coupling between pseudospins and phonons.
Authors:
 [1] ; ;  [2]
  1. School of Basic Sciences, Indian Institute of Technology Mandi, Mandi-175005 (India)
  2. Department of Physics, Indian Institute of Science, Bangalore-560012 (India)
Publication Date:
OSTI Identifier:
22454484
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 5; Journal Issue: 3; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMMONIA; ARSENATES; COUPLING; CRYSTALS; FERROELECTRIC MATERIALS; ORTHORHOMBIC LATTICES; PHASE TRANSFORMATIONS; PHONONS; POTASSIUM COMPOUNDS; PROTONS; SELF-ENERGY; SIGNALS; TEMPERATURE DEPENDENCE; TRANSITION TEMPERATURE