Sains Malaysiana 42(8)(2013): 1139–1144

Microstructural and Nonlinear Electrical Properties of ZnO Ceramics with Small

Amount of MnO₂ Dopant

(Sifat Mikrostruktur dan Elektrik Tak-linear Seramik ZnO  dengan

Kuantiti Kecil Dopan MnO₂)

A.N. Fauzana, B.Z. Azmi^* & M.G.M. Sabri

Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, D.E. Malaysia

W.R. Wan Abdullah & M. Hashim

Materials Synthesis and Characterization Laboratory, Institute of Advanced Technology

Universiti Putra Malaysia, 43400 UPM Serdang, Selangor D.E. Malaysia

Received: 27 June 2012 /Accepted: 16 December 2012

ABSTRACT

A small amount of MnO₂ dopant was added to ZnO system to see the improvement of the ceramic varistor microstructural and nonlinear electrical properties. The samples were prepared using solid-state reaction method and the microstructure and nonlinear electrical properties of the ZnO-xMnO₂ system were investigated for × = 0.011 to 0.026 mol%, at three sintering temperatures, 1180°C, 1240°C and 1300°C for 1 and 2 h sintering time. The XRD and EDAX analyses showed that the main phase was ZnO while ZnMnO₃ and ZnMnO₇ as the secondary phases developed and distributed at the grain boundaries and triple point junction. The SEM observation revealed that prolonged sintering temperature and time improved the microstructure uniformity and strongly influences the nonlinear behavior of the samples. The maximum density and grain size have been observed at 92% of theoretical density and 10.8 μm, respectively and occur at the highest sintering temperature which is 1300°C. The value of nonlinear coefficient α is found to increase with the increase of MnO₂ doping level up to 0.016 mol% and drop with further doping level increment for all sintering temperatures and time.

Keywords: MnO₂; nonlinear coefficient; ZnO varistor

ABSTRAK

Kuantiti kecil bahan dop MnO₂ ditambah kepada sistem ZnO untuk melihat peningkatan sifat-sifat mikrostruktur dan keelektrikan tak-linear seramik varistor. Sampel telah disediakan melalui kaedah tindak balas keadaan pepejal dan ciri-ciri struktur-mikro dan elektrik tak-linear bagi sistem ZnO-xMnO₂ telah dijalankan untuk kuantiti kecil × = 0.011 sehingga 0.026 mol%, pada tiga suhu pensinteran, 1180°C, 1240°C dan 1300ºC dengan masa pensinteran 1 dan 2 jam. Analisis XRD dan EDAX menunjukkan bahawa fasa utama adalah ZnO manakala ZnMnO₃ dan ZnMnO₇ sebagai fasa kedua terbentuk dan tertabur di sempadan butiran dan titik simpang tiga. Pemerhatian melalui SEM menunjukkan bahawa pemanjangan suhu dan masa persinteran memperbaiki keseragaman mikrostruktur dan mempengaruhi kelakuan tak-linear sampel. Ketumpatan dan saiz butiran maksimum telah diperhatikan pada 92% daripada ketumpatan teori dan 10.8.μm, masing-masing, berlaku pada suhu pensinteran tertinggi iaitu 1300ºC. Nilai daripada pekali tak-linear α didapati meningkat dengan peningkatan paras dop MnO₂ sehingga tahap 0.016 mol% dan menurun dengan penambahan paras dop seterusnya untuk semua suhu dan masa pensinteran.

Kata kunci: MnO₂; Pekali tak-linear; varistor ZnO

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*Corresponding author; email: azmizak@gmail.com