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The CaMg 1 -x Cr 2 x /3 Si 2 O 6 (0 ≤ x ≤ 0.1) microwave dielectric ceramics were synthesized via conventional solid state reaction. In this study, the effects of Cr3+ substituting for Mg2+ on morphology, crystal structure and microwave dielectric properties of CaMg 1 -x Cr 2 x /3 Si 2 O 6 ceramics were explored. XRD diffraction patterns exhibited that the CaMg 1 -x Cr 2 x /3 Si 2 O 6 ceramics possessed the pure phase of CaMgSi 2 O 6 when x ≤ 0.06 and a small amount of secondary phase Ca 3 Cr 2 (SiO 4) 3 for 0.08 ≤ x ≤ 0.1. SEM micrographs revealed that the substitution of Mg2+ with Cr3+ could decrease the grain size. The apparent density was affected by the concentration of Mg vacancies. The correlation between crystal structure and microwave dielectric properties was investigated through the Rietveld refinement and Raman analysis. The microwave dielectric properties were mainly dependent on relative density, ionic polarizabilities, internal strain Ƞ, disordered structure and MgO 6 octahedron distortions. Finally, CaMg 1 -x Cr 2 x /3 Si 2 O 6 (x = 0.02) ceramics sintered at 1270 °C for 3 h exhibited excellent microwave dielectric properties of ε r = 8.06, Q × f = 89054 GHz, τ f = −44.92182 ppm/ºC. [ABSTRACT FROM AUTHOR]

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]

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]

Abstract The Ca 0.35 Li 0.25 Nd 0.35 Ti 1- x (Zn 1/3 Ta 2/3) x O 3 (0 ≤ x ≤ 0.12) ceramics were prepared using the solid-state reaction route. The influence of substitution of (Zn 1/3 Ta 2/3)4+ for Ti4+ on microstructure and microwave dielectric properties of Ca 0.35 Li 0.25 Nd 0.35 Ti 1- x (Zn 1/3 Ta 2/3) x O 3 (CLNT(ZT) x) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that the ceramics with x ≤ 0.06 were crystallized as an orthorhombic perovskite structure in Pnma space group. However, the secondary phase of Nd 2 Ti 2 O 7 was observed with properties of 0.08 ≤ x ≤ 0.12. The analysis results of Raman spectra revealed the existence of oxygen octahedral distortion and the short-range ordering occurred in CLNT(ZT) x ceramics with the change of (Zn 1/3 Ta 2/3)4+ content. The dielectric constant (ε r) increased firstly and then decreased gradually when substitution increased, and the variation of ε r was affected by the B-site bond valence. The quality factor value (Q × f) was improved by right amount of substitution when x ≤ 0.08, but deteriorated seriously as excessive (Zn 1/3 Ta 2/3)4+ content was added (x ≥ 0.10). The temperature coefficient of the resonant frequency (τ f) was effectively reduced from +90.9 ppm/ºC to +30.3 ppm/ºC with the increasing of substitution due to the declination of tolerant factor (t). At last, the CLNT(ZT)0.08 ceramics sintered at 1250 °C for 4 h exhibited the excellent comprehensive dielectric properties with ε r = 120.63, Q × f = 3889 GHz, τ f = +60.9 ppm/ºC. [ABSTRACT FROM AUTHOR]