Structure, bond features, and vibrational spectra of novel K2Bi(PO4)(MoO4) microwave dielectric ceramic with ultra-low sintering temperature

This paper presents a study on the microwave dielectric properties of K2Bi(PO4)(MoO4) (KBPM) ceramics prepared through the solid-state method. XRD refinement analysis confirmed the presence of the orthorhombic crystal structure of the ceramics, belonging to space group Ibca (#73), with only the K2Bi(PO4)(MoO4) phase observed. The ceramic sintered at 625 °C exhibited the most compact structure and demonstrated excellent microwave dielectric properties: εr = 8.37, Q × f = 42,500 GHz, and τf = −78.2 ppm/°C. The measured value of εr closely matched the theoretical value, indicating a strong correlation between polarization and the εr. The Q × f value was found to be influenced by the packing fraction, while the τf value showed an inverse relationship with the Mo–O bond valence. Analysis based on the P–V-L theory revealed the interconnected nature of ionicity, lattice energy, bond energy, and the εr, Q × f, and τf of the ceramics. Raman spectroscopy provided valuable insights into the lattice vibrations of the ceramics. Additionally, the KBPM ceramics were found to possess favorable chemical compatibility with silver, suggesting their potential application as ultra-low-temperature co-fired ceramics.