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LiNiPO 4 (LNP) ceramics were synthesized using a conventional solid-state reaction method and different sintering temperatures. Differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, and X-ray diffraction (XRD) measurements indicated that single-phase olivine (Pnma, No. 62) was formed above 750°C, and dense LNP ceramic with a theoretical density of more than 95% was obtained at 825°C. Raman and far-infrared (IR) vibrational modes were assigned and discussed in detail. The intrinsic dielectric properties of the samples were calculated using the four-parameter semi-quantum (FPSQ) model based on far-IR reflectance spectroscopy and were in good agreement with the measured values. A positive relationship existed between the Raman shift of the υ 1 mode (attributed to the symmetric vibration of [PO 4 ] 3− ) and the corrected permittivity, and the opposite correlation was observed between the quality factor (Q × f) and the damping of the υ s mode as well as the distortion of the [NiO 6 ] octahedra. The optimized microwave dielectric properties of the LNP ceramics sintered at 825°C include an ultralow dielectric constant (5.18) and a good quality factor (24 076 GHz, f = 17.2 GHz). K E Y W O R D Sdielectric properties, lattice vibrational characteristics, microwave dielectric ceramics, olivine type, structure-property relationship | 2529 XIAO et Al.

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