Transformation processes in LaAlO3: Neutron diffraction, dielectric, thermal, optical, and Raman studies

Hayward, S. A. and Morrison, F. D. and Redfern, S. A. T. and Salje, E. K. H. and Scott, J. F. and Knight, K. S. and Tarantino, S. C. and Glazer, A. M. and Shuvaeva, V. and Daniel, P. and Zhang, M. and Carpenter, M. A. (2005) Transformation processes in LaAlO3: Neutron diffraction, dielectric, thermal, optical, and Raman studies. Physical Review B, 72 (5). 054110. DOI 10.1103/PhysRevB.72.054110

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Abstract

The behavior of the Pm3¯m-R3¯c phase transition in LaAlO3 TC=813 K from differential scanning calorimetry measurements has been studied using temperature-dependent measurements of the crystal structure, dielectric relaxation, specific heat, birefringence, and the frequencies of the two soft modes via Raman spectroscopy. While all these experiments show behavior near TC consistent with a second-order Landau transition, there is extensive evidence for additional anomalous behavior below 730 K. Below this temperature, the two soft mode frequencies are not proportional to each other, the spontaneous strain is not proportional to the square of the AlO6 rotation angle, and anomalies are seen in the birefringence. Twin domains, which are mobile above 730 K, are frozen below 730 K. These anomalies are consistent with biquadratic coupling between the primary order parameter of the transition AlO6 rotation and a second process. From the dielectric results, which indicate a smooth but rapid increase in conductivity in the temperature range 500–800 K, we propose that this second process is hopping of intrinsic oxygen vacancies. These vacancies are essentially static below 730 K and dynamically disordered above 730 K. The interaction between static vacancies and the displacive phase transition is unfavorable. A similar anomaly may be observed in other aluminate perovskites undergoing the same transition.

Item Type:	Article
Uncontrolled Keywords:	2005 AREP 2005 P IA49
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences
Journal or Publication Title:	Physical Review B
Volume:	72
Page Range:	054110
Identification Number:	10.1103/PhysRevB.72.054110
Depositing User:	Sarah Humbert
Date Deposited:	25 Mar 2011 17:09
Last Modified:	23 Jul 2013 09:58
URI:	http://eprints.esc.cam.ac.uk/id/eprint/1673

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