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• 作者：J. M. Garc铆a-Lastra ; P. Garc铆a-Fern谩ndez ; F. Calle-Vallejo ; A. Trueba ; J. A. Aramburu ; M. Moreno
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：July 7, 2014
• 年：2014
• 卷：53
• 期：13
• 页码：6534-6543
• 全文大小：476K
• ISSN：1520-510X

文摘

The delicate balance between cooperative and local contributions in the ferroelectric distortions of BaTiO₃ is explored by means of ab initio calculations. As a salient feature, it is found that a single Ti⁴⁺ ion in BaTiO₃ is not allowed to move off-center at ambient pressure, while this is no longer true if the lattice is expanded by only 5%, stressing the high sensitivity of the local contribution to chemical and hydrostatic pressures. In order to further understand the effect of local contributions on the phase transition mechanism of ferroelectrics, we have investigated the surprising C_3v 鈫?C_4v 鈫?O_h local transformations occurring in the 10鈥?0 K temperature range for the MnCl₆^{5鈥?/sup> complex formed in KCl:Mn+ that mimic the behavior of BaTiO₃. From Boltzmann analysis of the vibronic levels derived from ab initio calculations and considering decoherence introduced by random strains, the present calculations reproduce the experimental phase sequence and transition temperatures. Furthermore, our calculations show that the off-center instability in KCl:Mn+ would be suppressed by reducing by only 1% the lattice parameter, a situation that then becomes comparable to that found for BaTiO₃ at ambient pressure. The present results thus stress the deep link between the structural phase transitions of ferroelectric materials and local phase transitions displayed by transition-metal impurities in insulators.}