Sains Malaysiana 45(8)(2016): 1281–1287

Influence of Crystal Structural Orientation on Impedance and Piezoelectric Properties of KNN Ceramic Prepared using Sol-Gel Method

(Pengaruh Orientasi Struktur Hablur ke atas Sifat Impedans dan Piezoelektrik Seramik KNN yang Disediakan menggunakan Kaedah Sol-Gel)

I. IZZUDDIN, M.H.H. JUMALI*, Z. ZALITA, J.N. HUWAIDA & R. AWANG

Pusat Pengajian Fizik Gunaan, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor, Malaysia

Received: 20 April 2015/Accepted: 26 November 2015

ABSTRACT

The aim of this study was to investigate the effect of structural orientation on the impedance and piezoelectric properties of Ka_0.5Na_0.5NbO₃ (KNN) ceramic synthesized using modified sol-gel method. Dried xerogel was heated at 800^oC for 90 min and the aggregates were grinded to powder form. SEM micrographs confirmed that the powder consist of bimodal particles in nm and μm size regimes. The powder was compacted into 13 mm diameter pellet and sintered at 1000^oC for 6 h. Then the pellets were poled at 4.0kV/mm at 100^oC for 30 min. The as-sintered pellets displayed different sizes of cuboidal granules forming a relatively dense sample. The XRD and Raman spectroscopy results confirmed the formation of perovskite KNN with monoclinic crystal structure. The compositional analysis using Vegard’s law showed that the K:Na ratio was 0.5:0.5. Dramatic intensity enhancement in (110) reflection and subsequent reduction in (100) reflection as observed in X-ray diffractograms for the poled pellet suggest permanent shift in crystal orientation. Consequently, the Nyquist impedance plot of a Debye type semicircular arc was altered to a combination of a depressed semicircular arc. Unlike the initial plot, the real impedance, Z′ exhibited frequency dependence at low frequency regime. In addition, the relaxation time, τ of KNN sample shifted to lower frequency after the structural re-orientation while piezoelectric constant, d33 along (110) direction significantly improved from 5 to 35 pC/N.

Keywords: Domain; d33 constant; nanosize; poling; Vegards law

ABSTRAK

Tujuan penyelidikan ini ialah untuk mengkaji kesan orientasi stuktur hablur ke atas sifat elektrik impedan dan piezoelektrik bagi seramik Ka_0.5Na_0.5NbO₃ (KNN) yang disintesis melalui kaedah sol gel yang diubah suai. Xerogel KNN yang telah kering dipanaskan pada suhu 800^oC selama 90 min dan agregat yang terhasil dikisar untuk menghasilkan serbuk KNN. Mikrograf SEM mengesahkan saiz partikel KNN yang disintesis terdiri daripada partikel bimod iaitu dalam rejim bersaiz nm dan μm. Seterusnya KNN dipadatkan ke bentuk pelet berdiameter 13 mm dan disinter pada suhu 1000^oC selama 6 jam diikuti dengan pengutuban pada 4kV/mm pada suhu 100^oC selama 30 min. Sampel KNN yang disinter menunjukkan pembentukan butiran kuboid pelbagai saiz yang secara relatifnya membentuk sampel yang tumpat. Hasil pencirian XRD dan Raman mengesahkan pembentukan perovskit KNN dengan struktur hablur monoklinik. Analisis komposisi menggunakan hukum Vegard menunjukkan nisbah bagi K:Na adalah 0.5:0.5. Peningkatan keamatan yang mendadak pada satah (110) dan penurunan ketara keamatan pada satah (100) seperti yang diperhatikan pada difraktogram sinar-X bagi pelet yang dikutubkan menandakan peralihan kekal terhadap orientasi hablur. Akibatnya, graf impedans Nyquist lengkungan semibulatan jenis Debye berubah kepada gabungan lengkungan semibulatan terhimpit dan permulaan bagi lengkungan lain pada frekuensi rendah. Tidak seperti plot yang asal, graf impedan nyata, Z′ adalah bebas frekuensi pada rejim frekuensi rendah. Selain itu, masa santaian, τ bagi sampel KNN berganjak kepada frekuensi yang lebih rendah selepas pengorientasi semula manakala pemalar piezoelektrik, d33 pada arah (110) menokok secara signifikan daripada 5 kepada 35 pC/N.

Kata kunci: Domain; hukum Vegards; pemalar d33; pengutuban; saiz nano

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*Corresponding author; email: hafizhj@ukm.edu.my