A low-firing melilite ceramic Ba2CuGe2O7 and compositional modulation on microwave dielectric properties through Mg substitution

Abstract

A melilite Ba2CuGe2O7 ceramic was characterized by low sintering temperature and moderate microwave dielectric properties. Sintered at 960 °C, the Ba2CuGe2O7 ceramic had a high relative density 97%, a low relative permittivity (εr) 9.43, a quality factor (Q×f) of 20,000 GHz, and a temperature coefficient of resonance frequency (τf) −76 ppm/°C. To get a deep understanding of the relationship between composition, structure, and dielectric performances, magnesium substitution for copper in Ba2CuGe2O7 was conducted. Influences of magnesium doping on the sintering behavior, crystal structure, and microwave dielectric properties were studied. Mg doping in Ba2CuGe2O7 caused negligible changes in the macroscopic crystal structure, grain morphology, and size distribution, while induced visible variation in the local structure as revealed by Raman analysis. Microwave dielectric properties exhibit a remarkable dependence on composition. On increasing the magnesium content, the relative permittivity featured a continuous decrease, while both the quality factor and the temperature coefficient of resonance frequency increased monotonously. Such variations in dielectric performances were clarified in terms of the polarizability, packing fraction, and band valence theory.

Ultralow-Temperature Synthesis and Densification of Ag2CaV4O12 with Improved Microwave Dielectric Performances

“…The enhanced density is due to the grain growth, which agrees well with the microstructure evolution. Several other materials in the literature, such as Sr 3 V 2 O 8 , Ba 2 CuGe 2 O 7 , Li 2 ZnGeO 4 , and AgPb 2 Mg 2 V 3 O 12 have also demonstrated similar phenomena. ,− …”

Enhanced Second-Harmonic-Generation Efficiency and Birefringence in Melillite Oxychalcogenides Sr2MGe2OS6 (M = Mn, Zn, and Cd)

“…Melilite-type oxides with a general formula AE 2 M II M IV 2 O 7 (AE = alkaline-earth metals or Eu; M II = divalent transition metals or Mg; M IV = IVA metals) represent a large family of NCS compounds displaying attractive physical properties of ionic conductive, microwave dielectric, antiferromagnetic, and NLO properties. − They belong to the tetragonal crystal system with an NCS space group of P 4̅21 m (no. 113), which features interwoven [M II M IV 2 O 7 ] 4– layers with the AE 2+ cations located between these layers to balance the charge.…”

A novel low permittivity microwave dielectric ceramic Sr2Ga2SiO7 for application in patch antenna

“…A maximum value of 96.1% (with a density of 4.3 g/cm 3 ) was obtained at 1330 • C. As well known, the phase purity and microstructural features (density or porosity, and size distribution) extrinsically exert influence on the microwave dielectric properties. [18][19][20] Based on the XRD and SEM analysis, single-phase Sr 2 Ga 2 SiO 7 ceramic with dense microstructures was obtained, suggesting that subsequent dielectric characterization is suitable. Prior to dielectric measurements, estimation of the theoretical performances was preferentially carried out based on the far-infrared reflectivity spectrum.…”