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

Diserahkan: 19 Mei 2008 / Diterima: 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 30oC, 1 MHz; temperature coefficient of capacitance (TCC) of -156 ppm/oC in the range of 30oC to 300oC at 1 MHz. Chemical doping was carried out at either A (Bi1.5Zn0.5-xMx)(Zn0.5Ta1.5)O7, or B site (Bi1.5Zn0.5)(Zn0.5-xMxTa1.5)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: Bi3Zn2-xCdxTa3O14 (0≤x≤0.5), Bi3Zn2-xMgxTa3O14(0≤x≤0.2), Bi3Zn2-xNixTa3O14 (0≤x≤0.4), Bi3Zn2-xPbxTa3O14 (0≤x≤0.3), Bi3Zn2-xCaxTa3O14 (0≤x≤0.3) and Bi3Zn2-xCuxTa3O14 (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 500oC. Between 100 kHz and 1000 kHz, non-frequency dependence was observed in the range of 100 – 300oC. An increase in dielectric loss below 10 kHz was observed. Dielectric loss decreased with frequencies when temperature was above 500oC.  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 Bi3Zn2-xCaxTa3O14. 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 30oC dan 1 MHz; pekali suhu kapasitan (TCC) sebanyak -156 ppm/oC dalam lingkungan 30oC hingga 300oC pada 1 MHz. Pengedopan secara kimia dilakukan sama ada di tapak A (Bi1.5Zn0.5xMx)(Zn0.5Ta1.5)O7, atau di tapak B (Bi1.5Zn0.5)(Zn0.5-xMxTa1.5)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: Bi3Zn2-xCdxTa3O14 (0≤x≤0.5), Bi3Zn2-xMgxTa3O14 (0≤x≤0.2), Bi3Zn2-xNixTa3O14 (0≤x≤0.4), Bi3Zn2-xPbxTa3O14 (0≤x≤0.3), Bi3Zn2-xCaxTa3O14 (0≤x≤0.3) dan Bi3Zn2-xCuxTa3O14 (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 500oC.  Antara 100 kHz and 1000 kHz, ketidak bergantungan frekuensi kelihatan dalam lingkungan 100 – 300oC. Peningkatan kehilangan dielektrik di bawah 10 kHz juga dapat diperhatikan. Kehilangan dielektrik menurun dengan frekuensi apabila suhu adalah di atas 500oC. 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 Bi3Zn2-xCaxTa3O14.   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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*Pengarang untuk surat menyurat; email: khawcc@mail.utar.edu.my

 

 

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