Synthesis and Microwave Dielectric Characterization of Ca 1-x Sr x TiO 3 , Low-Loss Ceramics

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RESEARCH PAPER

Synthesis and Microwave Dielectric Characterization of Ca1-xSrxTiO3, Low-Loss Ceramics Abid Zaman1 • Sarir Uddin2 • Nasir Mehboob1 Received: 31 March 2020 / Accepted: 16 September 2020 Ó Shiraz University 2020

Abstract Microwave dielectric ceramics in the Ca1-xSrxTiO3 (0 B x B 0.7) composition series were fabricated via conventional solid state, mixed oxides route. The structural, microstructural and microwave dielectric properties of the sintered samples were investigated. The XRD patterns revealed the formation of a single-phase perovskite-structured compositions calcined at 1000 °C for 3 h in air. The structure was observed to be transformed from noncentrosymmetric orthorhombic (Pnma) to centrosymmetric cubic (Pm3m) at 0.5 B x. Microwave dielectric properties like relative permittivity (er), quality factor (Qxf) and dielectric loss (tan d) were measured at relatively lower frequency for millimeter (mm) wave wireless applications. Keywords Microwave dielectrics  Perovskites  Solid state route  Structural transition

1 Introduction Microwave dielectric materials are frequently used in wireless communication devices and broadcasting systems (Sebastian 2008; Chen et al. 2015; Iqbal et al. 2011). The dielectric component used in these electronic devices for receiving and transmitting of signals is termed as dielectric resonator (DR) reported first by Richtmyer in 1939 (Richtmyer 1939). A dielectric material to be used as a resonator or dielectric antenna must satisfy three major criteria such as high relative permittivity (er * 50) required for miniaturization, high quality factor (Q 9 f * 5000 GH) for better selectivity and low temperature coefficient of resonant frequency (sf * 0 ppm/°C) required for thermal stability of the component (Sebastian 2008). Among oxides microwave dielectric materials, CaTiO3based compositions possess relatively better microwave dielectric properties (Sebastian 2008). Perovskite-structured CaTiO3 was discovered in the Ural Mountain of & Sarir Uddin [email protected] 1

Department of Physics, Riphah International University, Islamabad 44000, Pakistan

2

Department of Physics, Government College Hayatabad, Peshawar 25000, Pakistan

Russia by Gustav Rose in 1839 and named after a Russian mineralogist Count lev Aleksevich Von perovski (1792–1856) (Sebastian 2008). At temperature above 1580 K, CaTiO3 exits in ideal cubic perovskite structure with space group Pm3m, whereas at temperature below 1380 K, it is orthorhombic with space group of Pbnm (Ali and Yashima 2005). The existence of a tetragonal phase (I4/mcm) and of a body-centered orthorhombic phase (Cmcm) has also been reported at intermediate temperatures (Redfern 1996). CaTiO3 exhibits high relative permittivity (er * 160), better quality factor (Qxf * 7000 GHz) and an undesired large positive temperature coefficient of resonant frequency (sf * 850 ppm/ °C) (Zheng et al. 2005; Liao et al. 2011). The dielectric properties of CaTiO3 ceramics can be further improved by