Effect of Yttrium Doping in Barium Zirconium Titanate Ceramics: A Structural, Impedance, and Modulus Spectroscopy Study
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BARIUM zirconate titanate BaZrxTi1xO3 (BZT) ceramics are among the most studied ferroelectric materials with various potential electronic applications such as piezoelectric transducers, dynamic random access memory (DRAM), and tunable microwave devices, as well as electric energy storage units.[1–9] Because of their high dielectric constants, they are generally adopted for X7R multilayer ceramic capacitors (MLCCs). Removal of impurities and addition of doping in BZT ceramics are common ways to improve electric performance.[10] Rare-earth oxide is an important additive for MLCCs with base metal electrodes.[11] Trivalent rare-earth cations can behave as acceptors or donors depending on the site they occupy; the resulting electric properties will strongly depend on the size of the impurity cations.[12,13] The research literature confirms
TANMAYA BADAPANDA, Ph.D. Scientist, is with the Department of Physics, CV Raman College of Engineering, Bhubaneswar 752054, India. LAE´CIO SANTOS CAVALCANTE, Ph.D. Scientist, GERALDO EDUARDO DA LUZ Jr., and NOUGA CARDOSO BATISITA, Professors, are with the Universidade Estadual do Piauı´ , CCN-Quı´ mica, R. Joa˜o Cabral, P.O. Box 2231, Teresina, PI 64002-150, Brazil. Contact e-mail: [email protected] SHAHID ANWAR, Ph.D. Scientist, is with the Colloids and Materials Chemistry, Institute of Minerals and Materials Technology, Bhubaneswar 751013, Odisha, India. ELSON LONGO, Professor, is with the LIEC-Universidade Estadual Paulista, P.O. Box 355, 14801-907 Araraquara, SP, Brazil. Manuscript submitted February 8, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
that a rare-earth element combined with magnesium ions are dominant additives in forming a shell and the core–shell structure in barium titanate (BaTiO3) ceramics.[14] Rare-earth elements are known to exhibit useful functions for stabilizing the temperature dependence of a relative dielectric constant and lowering the dissipation factor in dielectric ceramics.[15,16] While the literature contains many reports on the electric behavior of rare-earth-modified BaTiO3 ceramics, there is a dearth of reports on rare-earth-doped BZT ceramics. In the literature,[17–21] few reports are available on the dielectric behavior study of different heterovalent substitutions such as yttrium [Y3+] ions in BZT ceramics. Again, interior defects such as A-site vacancies seriously influence ionic conductivity of ceramic materials.[22–24] Thus, a fundamental understanding of the conduction mechanism due to the lattice defects created at short and medium ranges is imperative.[25] These defects may also be responsible for dielectric relaxations in the high-temperature range. A complex impedance and modulus analysis is a powerful tool to separate grain boundary and grain–electrode effects which usually act as trap sites for defects.[26] Therefore, the current article contains a detailed explanation regarding the effect of the replacement of Ba2+ by Y3+ ions in the BZT system with the general stoichiometric formula [Ba1xY2x/3](Zr0.25Ti0.75)O3 (BYZT) ceramics with
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