This article explores the microwave dielectric properties of (La 1-x Nd x ) 2 (Zr 0.96 Ti 0.04 ) 3 (MoO 4 ) 9 (x=0.1,0.3,0.5, and 0.7) ceramics prepared by solid-state reaction. Utilizing the Rietveld refinement technique in XRD, the sample is identified as a trigonal crystal system belonging to the R 3 ¯ c space group. SEM analysis indicates that relative density has a significant impact on the ε r and Q×f of ceramics. The Q×f values of ceramics are closely related to the FWHM of the Raman spectra. At 750℃, (La 0.5 Nd 0.5 ) 2 (Zr 0.96 Ti 0.04 ) 3 (MoO 4 ) 9 ceramic exhibited excellent dielectric properties: ε r = 10.4 (±0.08), Q×f = 149,300 (±3211) GHz, τ f = −34.8 (±0.7) ppm/℃. To gain a deeper understanding of the intrinsic mechanisms governing the microwave dielectric properties of ceramics, analysis based on the P-V-L theory reveals that the La(Nd)-O bond and Mo-O bond contribute significantly to ε r and Q×f, respectively.
Zezhen Yin,Yun Zhang,Shihua Ding,Tianxiu Song,Xiaoning Li,Jiaying Dan
The solid-phase method was utilized to synthesize LiAl 1- x Be x O 2- x /2 and LiAl 1- x Ga x O 2 ceramics. By Phillips-Van Vechten-Levine (P-V-L) theory, a strong correlation between chemical bond characteristics and microwave dielectric properties was established. X-ray diffraction (XRD) analysis confirmed that all components formed single-phase solid solution with tetragonal structure. Using Be 2+ and Ga 3+ as substitutes, the differences in ionic radii produced diametrically opposite changes in cell volume. The relative density increased to 97.61 % (98.57 %) with the addition of Be 2+ (Ga 3+ ). According to the P-V-L theory, the variation of ε r was influenced by bond ionization. The introduction of different ions caused bond lengths variations, which in turn affected the lattice energy fluctuations. Importantly, this change more than doubled Q×f from 16,268 GHz to 37,015 GHz. Furthermore, the evolution of τ f can be elucidated by the bond energy. Sintered at 1250 °C, both LiAl 0.96 Be 0.04 O 1.98 and LiAl 0.98 Ga 0.02 O 2 demonstrated outstanding microwave dielectric properties, characterized by ε r = 5.83–6.08, Q×f = 32,727∼37,015 GHz, and τ f = −134.8∼-112.4 ppm/°C.
Lei Xiao,Qiang Li,Lianwen Deng,Sen Peng,Tulin Yi,Weichun Liu
Ba 1- x K x (Zn 1/3 Nb 2/3 )O 3- x /2 (BKZN, x = 0–0.2) ceramics were prepared by the high-temperature solid-state reaction method. Based on P–V–L theory, Raman vibration spectroscopy and X-ray photoelectron spectroscopy (XPS), this paper investigates the relationship between the internal and external factors of K + substitution in the Ba(Zn 1/3 Nb 2/3 )O 3 (BZN) ceramics and the microwave dielectric properties of the ceramics. X-ray diffraction (XRD) characterisation revealed that all samples were single phase with no impure phases. Replacing Ba 2+ with K + greatly reduced the sintering temperature and optimised the microwave dielectric properties of the ceramics. The dielectric constant ( ε r ) was closely related to the ion polarizability and density, and inversely proportional to Raman shift of the A 1g (O) peak. The quality factor ( Q × f ) depended largely on the lattice energy ( U b ) and the full width at half-maximum (FWHM) of A 1g (O) near 790 cm −1 . The temperature coefficient of the resonance frequency ( τ f ) could be inferred from the bond energy ( E b ) and oxygen octahedral distortion. Finally, outstanding microwave dielectric properties ( ε r = 40.83, Q × f = 71,658 GHz and τ f = 2.52 ppm/°C) were acquired for Ba 0.95 K 0.05 (Zn 1/3 Nb 2/3 )O 2.975 ceramics sintered at the optimum sintering temperature (1325 °C) for 4 h.
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