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The BaNdTiCrO (0 ≤ z ≤ 3.0) ceramics were prepared using the solid-state reaction route. The influence of substitution of Cr for Ti on microstructure and microwave dielectric properties of BaNdTiCrO (BNTC z) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that pure BaNdTiO phase with tungsten bronze structure existed for z ≤ 1, but the secondary phase BaTiO was observed for 1.5 ≤ z ≤ 3. The substitution of Cr for Ti was confirmed by the results of scanning electron microscopy and energy dispersive spectrometer. The dielectric constant ( ε ) was deteriorated with the increment of substitution which was in accord with the tendency of apparent density. The quality factor value ( Q× f) was improved by a small amount of substitution for z ≤ 0.5, but deteriorated seriously when excessive Cr content was added ( z > 0.5). The temperature coefficient of the resonant frequency ( τ ) was effectively reduced from + 63 ppm/°C to − 7.1 ppm/°C with the increase of substitution content. At last, the excellent dielectric properties with ε = 81.53, Q× f = 11,294 GHz and τ = + 39.2 ppm/°C were obtained as z = 0.5 sintered at 1420 °C for 2 h. [ABSTRACT FROM AUTHOR]

Low permittivity CaMg 1- x (Mn 1/2 Zn 1/2) x Si 2 O 6 (x = 0-0.1) ceramics were synthesized via the solid-state reaction process for the first time. The Rietveld refinement, complex chemical bond theory and Raman spectra were introduced to analyze the effects of Mn2+/Zn2+ co-substitution to microwave dielectric properties. XRD spectra indicate the CaMg 1- x (Mn 1/2 Zn 1/2) x Si 2 O 6 ceramics processed the pure phase of CaMgSi 2 O 6 when x ≤ 0.02 and a small volume of secondary phase Ca 2 MgSi 2 O 7 for 0.04 ≤ x ≤ 0.1. The variation of ε r can be put down to average bond iconicity and Raman shift. Total lattice energy and packing fraction are main influence factor of the Q × f value. The monotonous decrease of τ f is associated with total bond valence and full width at half maximum of Raman peak. Additionally, CaMg 1- x (Mn 1/2 Zn 1/2) x Si 2 O 6 (x = 0.02) ceramics sintered at 1280 °C for 3 h exhibited excellent microwave dielectric properties of ε r = 8.16, Q × f = 70187, τ f = −38.48 ppm/°C. [ABSTRACT FROM AUTHOR]

The CaMg 1- x Mn x Si 2 O 6 (x = 0–0.08)ceramics were reported here for the first time. The relationships among structural characteristics, vibrational modes and dielectric properties for the ceramics were researched based on complex chemical bond theory and Raman vibrational spectroscopy. The formation of a single phase with clinopyroxene structure when x = 0 to 0.08 was detected by X-ray diffraction. The monotonous increase of ε r is ascribed to the average bond covalency, polarizability and Raman shift. The Q × f value is influenced by total lattice energy and full width at half maximum of Raman spectra which are both connected with the intrinsic loss. The variation of τ f is related to thermal expansion coefficient and M1-site bond valence. Furthermore, the CaMg 0.98 Mn 0·02 Si 2 O 6 ceramic sintered at 1300 °C possessed optimal microwave dielectric properties of ε r = 8.01, Q × f = 83469 GHz and τ f = −45.27 ppm/°C. [ABSTRACT FROM AUTHOR]