An Unconventional Phase Transition in BaAl2O4 Driven by Two Competing Soft Modes
| Autor: | Ishii, Y., Mori, S., Nakahira, Y., Moriyoshi, C., Taniguchi, H., Moriwake, H., Kuroiwa, Y. |
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| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | Phys. Rev. B 93, 134108 (2016) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevB.93.134108 |
| Popis: | We investigated the temperature dependence of the superlattice intensity and thermal diffuse scattering intensity of BaAl2O4, which has a network structure with corner-sharing AlO4 tetrahedra, via synchrotron X-ray diffraction experiments. The temperature variation of the superlattice intensity revealed that the structural phase transition occurs at TC = 451.4 K from the P6322 parent crystal structure to the low-temperature superstructure with a cell volume of 2a x 2b x c. BaAl2O4 exhibits an unconventional structural phase transition driven by two competing soft modes, q1/2 ~ (1/2, 1/2, 0) and q1/3 ~ (1/3, 1/3, 0). When approaching the TC from above, the soft mode with q1/3 appeared first and was followed by the q1/2 soft mode. The thermal diffuse scattering intensities from both soft modes increased sharply at TC; therefore, both modes condensed simultaneously. The first principles calculation revealed that structural instabilities exist at the M- and K-points, at which the calculated imaginary frequencies are similar. The small energy difference of these structural instabilities generates the two competing soft modes and determines the eventual low-temperature crystal structure. Comment: 5 pages and 4 figures |
| Databáze: | arXiv |
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