Effects of Te6+ substitution on the sintering behavior, phase composition, Raman characteristics, and microwave dielectric properties of CoMoO4 ceramics

With the robust advancement of fifth-generation (5G) wireless communication and the steady progression of sixth-generation (6G) wireless communication toward practical implementation, the communication sector has imposed unprecedented requirements on microwave dielectric ceramics, particularly concerning their crucial performance parameters, including a suitable dielectric constant, ultra-low dielectric loss, and a near-zero temperature coefficient of resonant frequency. CoMo 1- x Te x O 4 ( x  = 0.01, 0.03, 0.05, 0.07) ceramics were successfully synthesized via the conventional solid-state reaction method. The mixed powders underwent pre-calcination at 500 °C, and the samples were subsequently sintered for 4 h within the temperature range of 550 °C to 650 °C. The results of X-ray diffraction (XRD) analysis and Rietveld refinement reveal that when x  ≤ 0.03, the obtained samples are monoclinic ceramic crystals belonging to the C 2/ m space group. When the Te 6+ content x  ≥ 0.05, a monoclinic crystal structure with the P 2/ c space group emerges. Moreover, at x  = 0.07, the quality factor of the sintered ceramic samples reaches its maximum value at 600 °C. According to scanning electron microscopy (SEM) analysis, the relative density has a significant impact on the dielectric constant and quality factor of the ceramics. Raman spectroscopy was utilized to probe the internal lattice vibration modes. The results demonstrate that the dielectric constant ( εᵣ ) of the ceramics exhibits a close correlation with the Raman spectral shifts, while the quality factor ( Q  ×  f ) is strongly associated with the full—width at half-maximum (FWHM) of the Raman peaks. At 600 °C, the CoMo 1- x Te x O 4 ceramics exhibit excellent dielectric properties: a dielectric constant ε r  = 9.13 (± 0.06), a quality factor Q  ×  f  = 84,224 (± 2301) GHz, and a temperature coefficient of resonant frequency τ f  = -72.8 (± 1.3) ppm/°C. The ionic polarizability and relative density are the primary determinants of ε r . The Q  ×  f is influenced by the packing density and relative density. Based on the P–V–L theory, the Mo–O bonds make a significant contribution to the quality factor ( Q  ×  f ) and the temperature coefficient of resonant frequency ( τ f ). Notably, at 600 °C, the ceramics still maintain an appropriate dielectric constant ( ε r ) and high-performance Q  ×  f values. This research holds an indispensable role in the development of ultra-low temperature co—fired ceramics (ULTCC).