Solid State Science and Technology, Vol. 15, No 1 (2007) 74-81

ISSN 0128-7389

74

 

PHASE STUDY AND ELECTRICAL PROPERTIES OF DIVALENT

DOPED NON-STOICHIOMETRIC BISMUTH ZINC NIOBATE CUBIC

PYROCHLORE

 

K. B. Tana, C. K. Leea, Z. Zainala, Y.P. Tana and S.A. Halimb.

aChemistry Department, Universiti Putra Malaysia,

43400 Serdang, Selangor, Malaysia.

bPhysics Department, Universiti Putra Malaysia,

43400 Serdang, Selangor, Malaysia.

 

ABSTRACT

A study of extrinsic doping is essential to elucidate relative ability of the pyrochlore

materials to accommodate various dopants in forming new solid solutions and to search

for improvement of electrical properties. Much reported stoichiometric cubic pyrochlore

Bi3Zn2Nb3O14 appears to contain ZnO as secondary phase. Reducing Zn content in

Bi3Zn2Nb3O14 resulted in Bi3Zn2-xNb3O14-x solid solutions where 0.04 < x < 0.31. The

phase pure material of composition Bi3Zn1.84Nb3O13.84 has been indexed on a cubic cell,

space group FD3M, with cell constant a = 10.5579 (4) Ǻ. Incorporation of divalent ions

Cu2+, Mg2+, Ca2+, Co2+, Pb2+, Cd2+ and Ni2+ in non-stoichiometric cubic pyrochlore

Bi3Zn1.84Nb3O13.84 has been studied. Extensive solid solutions were observed when

copper and cadmium were introduced as dopants where solid solution limits were

obtained at x = 0.5 and 0.4, respectively in Bi3Zn1.84-xNb3MxO13.84. Other divalent

dopants showed rather narrow solid solutions in the range of x = 0.15 to 0.25.

Conductivity Arrhenius plots of all the doped materials are linear and reversible on

heat-cool cycles with activation energy of 1.4-1.6 eV (x = 0.1). At the frequency of 100

kHz, these materials exhibit high relative permittivity (ε’) and low dielectric loss (tan δ)

with values in range of 50-100 and 0.001-0.015, respectively at 28 oC. A slight increase

in relative permittivity was observed in the doped materials except where Cd2+ and Ni2+

were dopants. Dielectric loss generally increases with increasing dopant content.

Copper doped solid solutions exhibit higher conductivity which could be associated

with lowering of activation energy (1.4-0.8 eV).

 

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