resumo
The effect of praseodymium (Pr), an amphoteric substituent, on phase transition, dielectric relaxation and electrical conductivity has been studied and analysed in 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3) TiO3 (BCZT) ceramics synthesized by a solid state reaction method. Structural investigations showed co-existence of two phases -tetragonal (P4mm) and rhombohedral (R3m) - for compositions with x < 0.05 wt% Pr. Temperature dependent dielectric studies revealed two phase transitions - rhombohedral (R) -> tetragonal (T) and T -> cubic (C) - that gradually evolved into one T -> C transition for x > 0.05 wt% Pr in BCZT. A dielectric relaxation behaviour was observed in the temperature range of 275-500 degrees C that was attributed to the localized relaxation process (short-range hopping motion of oxygen vacancies) in the bulk of the material. Grain and grain boundary conductivity evaluated from the impedance data revealed that Pr acts as a donor dopant for x <= 0.05 wt% while it is an acceptor for higher concentration, in accordance with XRD observations. Defect chemistry analysis for better interpretation of the acquired data is presented. Frequency and temperature dependent ac conductivity studies were also performed and the obtained activation energy values were associated with possible conduction mechanisms.
palavras-chave
BARIUM-TITANATE CERAMICS; POSITIVE-TEMPERATURE-COEFFICIENT; ELECTRICAL-CONDUCTIVITY MEASUREMENTS; GRAIN-BOUNDARY RESISTIVITIES; DOPED BATIO3 CERAMICS; STRONTIUM-TITANATE; DIELECTRIC-SPECTROSCOPY; IMPEDANCE SPECTROSCOPY; PHASE-TRANSITIONS; SPACE-CHARGE
categoria
Chemistry; Physics
autores
Coondoo, I; Panwar, N; Vidyasagar, R; Kholkin, AL
nossos autores
Andrei Kholkin
Investigador Principal
Indrani Coondoo
Investigador Júnior
Reddithota Vidyasagar
Bolseiro de pós-DoutoramentoGrupos
G2 - Materiais Fotónicos, Eletrónicos e Magnéticos
G4 - Materiais Renováveis e Economia Circular
agradecimentos
I. Coondoo and R. Vidyasagar would like to thank the Foundation for Science and Technology (FCT), Portugal, for the financial support through postdoctoral research grant SFRH/BPD/81032/2012 and SFRH/BPD/104887/2014, respectively. Part of this work was developed in the scope of Project CICECO-Aveiro Institute of Materials (ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and, when applicable, co-financed by FEDER under the PT2020 Partnership Agreement. The authors also thank M. A. Rafiq for acquiring the impedance data.