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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