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Subsolidus solution and ionic conductivity of rock-salt structured Li3+5xTa1−xO4 electroceramics

Shari S., Tan K. B., Khaw C. C., Zainal Z., Lee O. J., Chen S. K.

Materials Science Poland

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2020

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Vol. 38, No. 3

465--474

EN

Lithium tantalate solid solution, Li3+5xTa1−xO4 was prepared by conventional solid-state reaction at 925 °C for 48 h. The XRD analysis confirmed that these materials crystallized in a monoclinic symmetry, space group C2/C and Z = 8, which was similar to the reported International Crystal Database (ICDD), No. 98-006-7675. The host structure, β-Li3TaO4 had a rock-salt structure with a cationic order of Li+:Ta5+ = 3:1 over the octahedral sites. A rather narrow subsolidus solution range, i.e. Li3+5xTa1−xO4 (0 ⩽ x ⩽ 0.059) was determined and the formation mechanism was proposed as a replacement of Ta5+ by excessive Li+, i.e. Ta5+ ↔ 5Li+. Both Scherrer and Williamson-Hall (W-H) methods indicated the average crystallite sizes in the range of 31 nm to 51 nm. Two secondary phases, Li4TaO4.5 and LiTaO3 were observed at x = 0.070 and x = −0:013, respectively. These materials were moderate lithium ionic conductors with the highest conductivity of ~2.5 × 10-3 Ω -1∙cm-1 at x = 0, at 0 °C and 850 °C; the activation energies were found in the range of 0.63 eV to 0.68 eV.

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High temperature impedance spectroscopy study of non-stoichiometric bismuth zinc niobate pyrochlore

Tan K. B., Khaw C. C., Lee C. K., Zainal Z., Tan Y. P., Shaari H.

Materials Science Poland

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2009

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Vol. 27, No. 3

825--837

EN

Single phase non-stoichiometric bismuth zinc niobate, Bi3Zn1.84Nb3O13.84, was fabricated by a conventional solid state method. The sample was refined and fully indexed on the cubic system, space group Fd3m (No. 227), Z = 4 with A = 10.5579(4) A. Electrical characterisation was performed using an ac impedance analyser over the temperature range of 25-850 °C and frequency range of 5 Hz-13 MHz. Typical dielectric response is observed in Bi3Zn1.84Nb3O13.84 with a high relative permittivity, low dielectric loss and a negative temperature coefficient of capacitance, with the values of 147, 0.002 and -396 ppm/°C, at 100 kHz at ambient temperature, respectively. This material is highly resistive, with a conductivity of 1×10-21 A-1 Acm-1 and a high activation energy of ca. 1.59 eV.

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High temperature impedance spectroscopy study of non-stoichiometric bismuth zinc niobate pyrochlore

Tan K. B., Khaw C. C., Lee C. K., Zainal Z., Tan Y. P., Shaari H.

Materials Science Poland

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2009

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Vol. 27, No. 4/1

947--959

EN

Single phase non-stoichiometric bismuth zinc niobate, Bi3Zn1.84Nb3O13.84 was prepared by a conventional solid state method. The sample was refined and fully indexed on the cubic system, space group Fd3m, Z = 4 with a = 10.5579(4) A. Electrical characterisation was performed using an ac impedance analyser over the temperature range of 25-850 °C and frequency range of 5 Hz - 3 MHz. Typical dielectric response was observed in Bi3Zn1.84Nb3O13.84with high relative permittivity, low dielectric loss and negative temperature coefficient of capacitance, with the values of 147, 0.002 and -396 ppm/°C, at 100 kHz at ambient temperature, respectively. The material is highly resistive, with the conductivity of 10-21 ohm-1ocm-1 and a high activation energy of 1.59 eV.