Effect of Sr2+ substitution on crystal structure, Raman characteristics and microwave dielectric properties of KCa1-xSrxPr(MoO3)4 ceramics for ULTCC applications

In this study, Sr 2+ was employed to substitute Ca 2+ in KCaPr(MoO 3 ) 4 ceramics. Such ion substitution was found to effectively enhance the Q × f value of KCaPr(MoO 3 ) 4 and moderately decrease its sintering temperature. Scanning electron microscopy (SEM) observations and density measurements indicated satisfactory sintering characteristics of this series of ceramics. Meanwhile, X-ray diffraction (XRD) and Raman spectroscopy analyses suggested the formation of a solid solution without obvious secondary phases or impurities, verifying the successful preparation of single-phase molybdate ceramics. On the basis of P–V–L theoretical analysis, it was suggested that K/Ca/Pr–O bonds mainly contribute to the bond ionicity (fᵢ), whereas Mo–O bonds exert considerable influences on the lattice energy (U), bond energy (E), and thermal expansion coefficient (α). Among the as-prepared ceramic samples, KCa 0.98 Sr 0.02 Pr(MoO 3 ) 4 exhibited the most favorable dielectric properties at 700 ℃ with a relative permittivity (εᵣ) of 10.744, a quality factor-frequency product (Q ×  f ) of 89 349 GHz, and a temperature coefficient of resonant frequency (τ f ) of − 59.947 ppm/  C. Benefiting from the ion substitution strategy, the obtained materials possessed relatively low sintering temperatures and high Q ×  f values, suggesting promising potential for application in ultra-low-temperature co-fired ceramics (ULTCC).