Investigation of crystal structure and chemical bonds characteristics on microwave properties of novel Ca-doped Sr1–xCaxTm2O4 (x=0.025–0.300) ceramics

Abstract

Dense microwave dielectric ceramics of Sr_1–xCa_xTm₂O₄ (x = 0.025–0.300) were fabricated via the conventional solid-state reaction method. Systematical investigations on the impact of Ca²⁺ on their microstructures, sintering behaviors, and microwave dielectric properties were detailly conducted. The combined XRD data and subsequent refinement demonstrated that all samples exhibited structural conformity with SrTm₂O₄ and belonged to Pnam space group. Calculations were executed to illustrate the evolution of performance-related chemical bonding parameters associated with Ca²⁺ on the basis of the PVL theory. High density, lattice energy and narrow full width at half maximum of Raman modes contribute to a performance boost of around 14%. Excellent dielectric properties of Sr_0.95Ca_0.05Tm₂O₄, including relative permittivity of 15.97, quality factor of 47,142 GHz, and temperature coefficient of resonant frequency of –24.65×10⁻⁶ °C^–1. Furthermore, Sr_0.95Ca_0.05Tm₂O₄ ceramics were designed as rectangular dielectric resonator antennas with 388 MHz bandwidth at the center frequency of 6.525 GHz, along with high simulated radiation efficiency (≥ 90%) and realized gain (5.80–6.47 dBi), which suggests their considerable potential in 5G communication applications.