Analysis of the Crystal Structure and the Relation with the Temperature Coefficient <TEX>au_varepsilon$</TEX> in <TEX>$BaORe_2O_3TiO_2$</TEX> (Re=La, Nd, Y) Microwave Dielectric Ceramics

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J. Korean Ceram. Soc. > Volume 36(2); 1999 > Article

Journal of the Korean Ceramic Society 1999;36(2): 136.

$BaORe_2O_3TiO_2$ (Re=La, Nd, Y)계 고주파 유전체의 결정구조 분석 및 온도계수 au_varepsilon$와의 관련성

김정석, 강현주, 심해섭¹, 이창희¹, 천채일

호서대학교 재료화학공학부
¹한국원자력연구소 하나로센터 중성자 물리실

Analysis of the Crystal Structure and the Relation with the Temperature Coefficient au_varepsilon$ in $BaORe_2O_3TiO_2$ (Re=La, Nd, Y) Microwave Dielectric Ceramics

ABSTRACT

Crystal structures of tungsten-bronze type microwave dielectric ceramics, $BaOLa_2O_34TiO_2$ (BLT) and $BaO(Nd_{0.77}Y_{0.23})_4TiO_2$ (B(NY)T), were analysed using the Rietveld method. The most relibale refinement was obtained by refining the cation and anion positions from the x-ray and neutron diffraction data, respectively. The ambiguites inherent in the refined crystal structure by Mateeva et al. were resolved. The $BaORe_2O_34TiO_2$ structure consiste of $3times2$ perovskite blocks and 4 pentagon-channels. The Ti-O6 octahedrons are distroted and tilted, which, consequently, induces the displacements of Ba and Re ions producing the superlattics (c$approx$ 7.6 $AA$). The B(NY)T showed more severely tilted Ti-O6 octahedrons. The relative dielectric constant $varepsilon_{gamma}$ and temperature coefficient $tau_varepsilon$ are 109.5 and-$180 ppm/^{circ}C$ in BLT, 76 and $+40 ppm/^{circ}C$ in B(NY)T, respectively. The small Re ions produced a positive $tau_varepsilon$. The relation between $tau_varepsilon$ and the octahedron tilting in complex perovskite is discussed for the tungsten bronze type structure.

Key words: crystal structure, $BaORe_2O_3TiO_2$ (Re=La, Nd, Y), Temperature coefficient of dielectric constant, Octahedron tilting