Sains Malaysiana 38(3): 387-393(2009)

Synthesis and Characterisation of Cubic Bi₃Zn₂Ta₃O₁₄ and

its Related Divalent-Doped Pyrochlore Materials

(Sintesis dan Pencirian Kubus Bi₃Zn₂Ta₃O₁₄ dan Pengedopan

Dwivalen Bahan Piroklor Berkaitan)

Khaw Chwin Chieh*

Faculty of Engineering and Science, UTAR Complex, Jalan Genting Klang

53300 Setapak, Kuala Lumpur, Malaysia

Tan Kar Ban, Zulkarnain Zainal

Chemistry Department, Faculty of Science

43400 UPM Serdang, Selangor D.E., Malaysia

Lee Chnoong Kheng

Academy of Sciences Malaysia , 902-4, Jalan Tun Ismail
50480 Kuala Lumpur, Malaysia

Received: 19 May 2008 / Accepted: 9 September 2008

  ABSTRACT

Bi₃Zn₂Ta₃O₁₄, ‘P’, was crystallised in a cubic unit cell with lattice parameter of a=10.5437 (9) Å. The material had permittivity, ε’, of around 58 and dielectric loss, tan δ, of 2.3 × 10^-3 at 30^oC, 1 MHz; temperature coefficient of capacitance (TCC) of -156 ppm/^oC in the range of 30^oC to 300^oC at 1 MHz. Chemical doping was carried out at either A (Bi_1.5Zn_0.5-xM_x)(Zn_0.5Ta_1.5)O₇, or B site (Bi_1.5Zn_0.5)(Zn_0.5-xM_xTa_1.5)O₇ in search of better performance materials. Various divalent cations such as Cd²⁺, Ca²⁺, Mg²⁺, Ni²⁺, Pb²⁺, and Cu²⁺ were used as dopants. Solid solutions formed were: Bi₃Zn_2-xCd_xTa₃O₁₄ (0≤x≤0.5), Bi₃Zn_2-xMg_xTa₃O₁₄(0≤x≤0.2), Bi₃Zn_2-xNi_xTa₃O₁₄ (0≤x≤0.4), Bi₃Zn_2-xPb_xTa₃O₁₄ (0≤x≤0.3), Bi₃Zn_2-xCa_xTa₃O₁₄ (0≤x≤0.3) and Bi₃Zn_2-xCu_xTa₃O₁₄ (0≤x≤0.1).  Electrical properties of the materials were investigated using impedance spectroscopy. Conductivities of the solid solutions were higher than that of the parent material Bi₃Zn₂Ta₃O₁₄. These doped materials exhibited similar behaviour as Bi₃Zn₂Ta₃O₁₄, showing a high degree of dispersion of permittivity at low frequencies (<1 kHz) and at temperatures above 500^oC. Between 100 kHz and 1000 kHz, non-frequency dependence was observed in the range of 100 – 300^oC. An increase in dielectric loss below 10 kHz was observed. Dielectric loss decreased with frequencies when temperature was above 500^oC.  Dielectric loss of all divalent cation doped materials was higher than that of the parent material; maximum permittivity value of 68 was recorded at x = 0.3 in Bi₃Zn_2-xCa_xTa₃O_14. TCC obtained in this study had negative values; no obvious correlation between TCC and composition of the doped materials can be deduced.

Keywords: Dielectric loss; permittivity; pyrochlore; temperature coefficient of capacitance

ABSTRAK

Bi₃Zn₂Ta₃O₁₄, ‘P’, dihablurkan dalam sel unit kubus dengan parameter kekisi a=10.5437 (9) Å. Bahan ini mempunyai permitiviti, ε’, dengan nilai 58, kehilangan dielektrik, tan δ, sebanyak 2.3 × 10^-3 pada 30^oC dan 1 MHz; pekali suhu kapasitan (TCC) sebanyak -156 ppm/^oC dalam lingkungan 30^oC hingga 300^oC pada 1 MHz. Pengedopan secara kimia dilakukan sama ada di tapak A (Bi_1.5Zn_0.5xM_x)(Zn_0.5Ta_1.5)O₇, atau di tapak B (Bi_1.5Zn_0.5)(Zn_0.5-xM_xTa_1.5)O₇ dengan tujuan mencari bahan dengan prestasi yang lebih baik. Pelbagai kation dwivalensi seperti Cd²⁺, Ca²⁺, Mg²⁺, Ni²⁺, Pb²⁺, and Cu²⁺ digunakan sebagai dopan. Larutan pepejal terbentuk adalah: Bi₃Zn_2-xCd_xTa₃O₁₄ (0≤x≤0.5), Bi₃Zn_2-xMg_xTa₃O₁₄ (0≤x≤0.2), Bi₃Zn_2-xNi_xTa₃O₁₄ (0≤x≤0.4), Bi₃Zn_2-xPb_xTa₃O₁₄ (0≤x≤0.3), Bi₃Zn_2-xCa_xTa₃O₁₄ (0≤x≤0.3) dan Bi₃Zn_2-xCu_xTa₃O₁₄ (0≤x≤0.1). Sifat elektrik bagi bahan-bahan tersebut disiasat dengan spektroskopi impedans. Kekonduksian bagi larutan pepejal adalah lebih tinggi daripada bahan induk Bi₃Zn₂Ta₃O₁₄. Bahan-bahan didop menunjukkan ciri yang sama seperti Bi₃Zn₂Ta₃O₁₄, menunjukkan satu ketelusan sebaran yang tinggi pada frekuensi rendah (<1 kHz) dan pada suhu di atas 500^oC.  Antara 100 kHz and 1000 kHz, ketidak bergantungan frekuensi kelihatan dalam lingkungan 100 – 300^oC. Peningkatan kehilangan dielektrik di bawah 10 kHz juga dapat diperhatikan. Kehilangan dielektrik menurun dengan frekuensi apabila suhu adalah di atas 500^oC. Kehilangan dielektrik bagi semua bahan yang didop dengan kation dwivalensi adalah lebih tinggi daripada bahan induk; ketelusan maksimum dengan nilai 68 direkodkan pada x = 0.3 in Bi₃Zn_2-xCa_xTa₃O_14.   TCC yang didapati dalam kajian ini mempunyai nilai negatif; tiada hubungan antara TCC dengan komposisi bahan-bahan yang didop.

Kata kunci: Ketelusan; kehilangan dielektrik; pekali suhu kapasitan; Piroklor

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*Corresponding author; email: khawcc@mail.utar.edu.my