Role of Bi 2 O 3 in optimizing the dielectric properties of Ba 4.5 Nd 9 Ti 18 O 54 based microwave ceramics

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imizing the dielectric properties of Ba4.5Nd9Ti18O54 based  microwave ceramics Matjaž Valant, Danilo Suvorov and Drago Kolar Journal of Materials Research / Volume 11 / Issue 04 / 1996, pp 928 ­ 931 DOI: 10.1557/JMR.1996.0116

Link to this article: http://journals.cambridge.org/abstract_S0884291400023098 How to cite this article: Matjaž Valant, Danilo Suvorov and Drago Kolar (1996). Role of Bi2O3 in optimizing the dielectric properties of Ba4.5Nd9Ti18O54  based microwave ceramics. Journal of Materials Research,11, pp 928­931 doi:10.1557/JMR.1996.0116 Request Permissions : Click here

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Role of Bi2 O3 in optimizing the dielectric properties of Ba4.5 Nd9 Ti18 O54 based microwave ceramics Matjaˇz Valant, Danilo Suvorov, and Drago Kolar Department of Ceramics, “Joˇzef Stefan” Institute, University of Ljubljana, Ljubljana, Slovenia (Received 21 November 1994; accepted 5 December 1995)

Small additions of Bi2 O3 or bismuth titanate improve the dielectric properties of Ba4.5 Nd9 Ti18 O54 at microwave frequencies. It was found that Bi31 can replace Nd31 up to 15 mol %, the limiting composition of solid solution being Ba4.5 (Nd0.85 Bi0.15 )9 Ti18 O54 . At the solid solution limit the temperature coefficient of resonant frequency attains its minimum value. The modified ceramic is distinguished by high permittivity of 99 and a Q-value of 5500. The temperature coefficient of resonant frequency is low, 15 ppmyK. After exceeding the solid solubility limit, additional Bi2 O3 concentrates as a Bi-rich phase at the grain boundaries, causing considerable reduction of the Q-value and an increase of tf . I. INTRODUCTION

Ceramics based on the BaO–Nd2 O3 –TiO2 system are widely used in the electronics industry, due to their high permittivity (.85) and low dielectric losses. An especially interesting part of the phase diagram is the solid solubility region with general formula Ba62x Nd812/3x Ti18 O54 (0 , x , 2.25).1 Variation of stoichiometry requires the possibility of partial replacement of Ba21 with Nd31 cations in a perovskite-like structure.2–4 Crystal structure determinations indicate the existence of a chemical composition close to Ba4.5 Nd9 Ti18 O54 with a molar ratio BaO : Nd2 O3 : TiO2 ­ 1 : 1 : 4 commonly known as “114” or “BNT4 ”. The Ba4.5 Nd9 Ti18 O54 exhibits very promising dielectric properties in the microwave frequency range. Its permittivity, measured at 3 GHz, is 80.8 and the Q-value 3500.5 Since the temperature coefficient of resonant frequency is rather high (93 ppmyK), it must be decreased by compositional modification. Wakino et al.5 improved tf by partial replacement of Ba21 with Pb21 and adjusting the composition to produce a small amount of Nd2 Ti2 O7 secondary phase. Negas et al. tuned the tf of Sm-based 114 compound by adjusting the TiO2 content along the join TiO2 –114.6 A very important microwave dielectric property, besides permittivity and temperature stabili

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