$(Pb,Ca)ZrO_3$ ceramics (PCZ) has high dielectric constant, high quality factor and small temperature coefficient of resonant frequency in microwave frequency range. But the basic properties such as crystal structure, phase transition and mechanism of temperature characteristics of dielectric properties were not fully understood.
We investigated the crystallographic structure, dielectric properties and sintering behavior of $(Pb_{1-x}Ca_x)(Zr_{1-y}Sn_y)O_3$ ceramics (PCZS) fabricated by mixed oxide method.
The crystallographic structure of the PCZS ceramics was refined by X-ray Rietveld method to be orthorhombic, Cmcm space group. the mmm point group of PCZS ceramics was investigated by convergent beam electron diffraction.
The loss of PbO during sintering of PCZS ceramics deteriorates the electrical and mechanical properties of specimen. Ca and Sn substitution decrease the loss of PbO. The inhibit of PbO vaporization was effectively achieved by Sn rather than Ca substitution.
To adapt the PCZS ceramics to resonators and filters in microwave frequency range, the temperature coefficient of resonant frequency should be precisely controlled. Because the temperature coefficient of resonant frequency is a function of the temperature coefficient of dielectric properties of dielectric constant and linear thermal expansion coefficient of the materials used, the temperature coefficient of dielectric constant was measured and analyzed on the basis of crystallographic structure change. The dielectric constant was decreased as Ca, Sn substitution. It was explained by smaller ionic polarizability of $Ca^{2+}$ and $Sn^{4+}$ than that of $Pb^{2+}$ and $Zr^{4+}$ ions. There were two types of phase transition in the temperature range from -140℃ and 350℃. The phase transition temperature of the PCZS ceramics was changed due to the modifications of crystallographic structure. The nature of these phase transition of PCZS ceramics was the key parameters which controlled the temperature coefficient of dielectric constant.
