Chemical mixing and hard mode spectroscopy in ferroelastic lead phosphate arsenate: local symmetry splitting and multiscaling behaviour

Salje, E. K. H. and Beirau, T and Mihailova, B and Malcherek, T and Bismayer, U (2010) Chemical mixing and hard mode spectroscopy in ferroelastic lead phosphate arsenate: local symmetry splitting and multiscaling behaviour. Journal of Physics: Condensed Matter, 22 (4). 045403. DOI 10.1088/0953-8984/22/4/045403

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Abstract

The phase transition in ferroelastic Pb 3 ( PO 4 ) 2 –Pb 3 ( AsO 4 ) 2 mixed crystals shows typical multiscaling behaviour with two relevant length and timescales. One length scale is macroscopic and shows uniform, weakly first-order phase transitions between a rhombohedral paraphase (R ¯ 3m) and a monoclinic ferroelastic phase (C2 / c). The second length scale is on the level of tetrahedral complexes which display monoclinic distortions at temperatures well above the macroscopic transition point. For instance, in Pb 3 ( P 0 . 43 As 0 . 57 O 4 ) 2 the AsO 4 polyhedra show static deformation up to ∼ 60 K above the deformation of the PO 4 tetrahedra. The two timescales are either short compared with the time of observation, namely the dynamic reorientation of the PO 4 tetrahedral distortion, or very long. The long timescale refers then to the (quasi)static distortion of the AsO 4 tetrahedra which persists at T > T c . These distortions appear to be uncorrelated or only weakly correlated and their random field leads to an order/disorder aspect of the phase transition which remains, on a phonon timescale, essentially displacive in character.

Item Type:	Article
Uncontrolled Keywords:	09AREP;
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences
Journal or Publication Title:	Journal of Physics: Condensed Matter
Volume:	22
Page Range:	045403
Identification Number:	10.1088/0953-8984/22/4/045403
Depositing User:	Sarah Humbert
Date Deposited:	23 Mar 2012 16:18
Last Modified:	23 Jul 2013 10:03
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2427

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