Low-permittivity NaLaP2O7 ceramics sintered at 750 °C: unraveling structure-property relationships through Rietveld refinement, Raman spectroscopy, and P-V-L chemical bond analysis

A novel NaLaP 2 O 7 ceramic was fabricated via the solid-state reaction method. The sample sintered at 750 °C demonstrated optimal microwave dielectric properties with an ε r of 7.3, a high Q × f value of 23,510 GHz, and a τ f of –79.3 ppm/°C, which are attributed to its high relative density (95.3%) and homogeneous microstructure. Rietveld refinement confirmed a pure orthorhombic phase ( Pnma ). Furthermore, chemical bond analysis based on the P-V-L theory revealed that the high ionicity of La–O bonds predominantly governs the permittivity, while the strong lattice energy and bond energy of P–O bonds are responsible for the high Q × f value and thermal stability, respectively. Raman spectroscopy further verified the highly ordered crystal structure, shown by the characteristic vibrational modes of the P 2 O 7 4- dimer. These findings not only demonstrate that NaLaP 2 O 7 ceramic is a promising low-permittivity candidate for LTCC applications in millimeter-wave communication, but also provide deep insights into the underlying structure–property relationships.