Dielectric and infrared response of Ba0.77Ca0.23TiO3

• Published in: Ferroelectrics Vol. 295; pp. 31 - 38
• Main Authors: Savinov, M E, Trepakov, V A, Kamba, S, Kapphan, S E, Petzelt, J, Pankrath, R, Kislova, I L, Kutsenko, A B, Jastrabik, L
• Format: Journal Article
• Language: English
• Published: 01-01-2003
• ISSN: 0015-0193
• DOI: 10.1080/00150190390239431

Low-frequency (100 Hz-I MHz) dielectric permittivity and infrared reflectivity studies were performed for barium-calcium-titanate single crystals of the congruently melting composition Ba0.77Ca0.23TiO3, nominally pure (BCT77/23) and doped by Cr (70 ppm, BCT77/23:Cr). Both the materials reveal a sharp *e'(T) maximum at 375 K (cooling run) with a pronounced temperature hysteresis, evidencing a first-order ferroelectric phase transition (PT)Oh RT C4V. The high-temperature wing of the *e'(T) maximum reveals a weak dispersion of a non-relaxation nature. The low-temperature wing contains a reproducible step in the *e'(T) dependence. Another low-temperature PT was found at ~41K. Cr doping strongly influences this PT shifting the position of the *e'(T) maximum to ~20K. Polarised IR reflectivity shows a huge A1 - E splitting of TO1 polar phonons below the ferroelectric PT as in the pure BaTiO3. IR spectra indicate a displacive and diffuse character for the low temperature PT, but leave open the question about the predominance of displacive or order-disorder character of the high temperature PT.