Peculiar Bi-ion dynamics in Na sub(1/2)Bi sub(1/2)TiO sub(3) from terahertz and microwave dielectric spectroscopy

• Published in: Phase transitions Vol. 87; no. 10-11; pp. 953 - 965
• Main Authors: Petzelt, Jan, Nuzhnyy, Dmitry, Bovtun, Viktor, Pasciak, Marek, Kamba, Stanislav, Dittmer, Robert, Svirskas, Sarunas, Banys, Juras, Rodel, Juergen
• Format: Journal Article
• Language: English
• Published: 02.11.2014
• Subjects: Anharmonicity; Dielectric constant; Dielectric strength; Dielectrics; Dynamics; Oscillators; Permittivity; Retarding
• ISSN: 0141-1594; 1029-0338
• DOI: 10.1080/01411594.2014.953517

Dynamics of the main dielectric anomaly in Na sub(1/2)Bi sub(1/2)TiO sub(3) (NBT) were studied by time-domain THz and microwave spectroscopy, using also previously published data and their new overall fits. Above the dielectric maximum temperature T sub(m) approximately 600 K, the response consists of coupled sub-THz oscillator and a relaxation mode, assigned to strongly anharmonic Bi-ion vibrations and hopping, whose slowing down explains the paraelectric-like permittivity increase to T sub(m). Below T sub(m), the main relaxation continues slowing down and additional relaxation, assigned to quasi-Debye losses, appears in the 10 super(11) Hz range. The oscillator hardens on cooling and takes over the whole oscillator strength. The permittivity decrease below T sub(m) is caused by the reduced strength of the relaxations due to dominance of the rhombohedral phase within the coexistence region with the tetragonal phase. The anharmonic dynamics of Bi are supported by previous structural studies. NBT represents a hybrid between standard and relaxor ferroelectric behaviour.