Structure, Raman spectra and microwave dielectric properties of novel garnet-type Ca₃MZrGe₃O₁₂ (M = Co, Zn) ceramics

Abstract

Two novel garnet-type ceramics Ca 3 MZrGe 3 O 12 (M = Co and Zn) with pure phase were prepared through a solid-state reaction method. Structure-property relationships were studied by the Rietveld refinement and Raman spectra. The appearance of two weak symmetric stretching vibrational peaks in Ca 3 ZnZrGe 3 O 12 might be due to the lower ordering. Higher Q × f value in Co-analogue was related to the larger packing fraction and the lower FWHM of A 1g mode. The smaller oxygen bond valence in Ca 3 CoZrGe 3 O 12 indicates a smaller τ f value. At the optimized sintering temperature of 1280 °C, Ca 3 CoZrGe 3 O 12 shows desirable microwave dielectric properties with ε r of 10.37, Q × f value of 60,100 GHz, and τ f value of −28.5 ppm/ o C. The Ca 3 ZnZrGe 3 O 12 ceramic sintered at 1200 °C has the best microwave dielectric properties with ε r of 10.48, Q × f value of 49,700 GHz, and τ f value of −35.8 ppm/ o C.

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

“…2e . These Raman peaks at 100−280 and 280−1000 cm −1 are assigned to the [CaO 8 ] and [GeO 4 ] sites, respectively (Table S5 ) 40 . Apparently, the intensity of these Raman signals becomes much lower after the cosubstitution of [Zn 2+ –Zr 4+ ] for [Y 3+ –Y 3+ ], which means weaker vibrations of Ca–O and Ge–O bonds in x = 1 41 .…”