Qing-Song Cao’s research while affiliated with Huazhong University of Science and Technology and other places

The ion valence state, phase composition, microstructure, and microwave dielectric properties of Sr (1-1.5x) Ce x TiO 3 (x = 0.1-0.67, SCT) ceramics were systematically investigated. Sr (1-1.5 x)Cex TiO 3 ceramics were produced with gradual structural evolution from a cubic to a tetragonal and turned to an orthorhombic structure in the range of 0.1 ≤ x ≤ 0.67. Above a critical Ce proportion (x = 0.4), microstructural changes and normal grain growth initially occurred. On the basis of chemical analysis results, the reduction of Ti 4+ ions was hastened by tetravalent ions (Ce 4+). By contrast, this reduction was inhibited by trivalent ions (Ce 3+). The observed dielectric behavior was strongly influenced by phase composition, oxygen vacancies (V O), and defect dipoles, namely, (Ti 0 À V O) and (V 00 Sr À V O). Temperature stable ceramics sintered at 1350°C for 3 h in air yielded an intermediate value of dielectric constant (e r = 40), with the smallest reported value of temperature coefficient of resonant frequency (s f = +0.9 ppm/°C), and quality factor (Q 3 f = 5699 GHz) at x = 0.6.

The ion valence state, phase composition, microstructure, and microwave dielectric properties of Sr(1-1.5x)CexTiO3 (x = 0.1-0.67, SCT) ceramics were systematically investigated. Sr(1-1.5x)CexTiO3 ceramics were produced with gradual structural evolution from a cubic to a tetragonal and turned to an orthorhombic structure in the range of 0.1 ≤ x ≤ 0.67. Above a critical Ce proportion (x = 0.4), microstructural changes and normal grain growth initially occurred. On the basis of chemical analysis results, the reduction of Ti4+ ions was hastened by tetravalent ions (Ce4+). By contrast, this reduction was inhibited by trivalent ions (Ce3+). The observed dielectric behavior was strongly influenced by phase composition, oxygen vacancies (VO), and defect dipoles, namely, (Ti'-VO) and (VSr″-VO). Temperature stable ceramics sintered at 1350°C for 3 h in air yielded an intermediate value of dielectric constant (εr = 40), with the smallest reported value of temperature coefficient of resonant frequency (τf = +0.9 ppm/°C), and quality factor (Q × f = 5699 GHz) at x = 0.6.

Low-temperature co-fired ceramics (LTCCs), with a Zn(Mn 1 À x Ti x) 3 O 7 (0rxr1.0) composition, were prepared using a conventional solid-state method. A novel ZnMn 3 O 7 ceramic was obtained, with a ZnMn 2 O 4 spinel structure, ε r of 7.32, Q Â f of 13,667 GHz, and τ f of À58.33 ppm/1C. The effect of various dopant concentrations on the microstructure and microwave dielectric properties of the material was investigated. Results showed that the increase in dopant concentration changed the phase composition, improved the microwave dielectric properties, and reduced the sintering temperature of the Zn(Mn 1 À x Ti x) 3 O 7 by a factor of 250 1C. The dielectric constant of Zn(Mn 1À x Ti x) 3 O 7 varied from 7.32 to 33.08 at x¼0.8. However, the maximum value was reduced to 27.67 at x¼ 1.0. Moreover, the value of Q Â f increased significantly up to a maximum value of 18,934 GHz, whereas τ f changed gradually from À58.33 ppm/1C to þ289.25 ppm/1C. In addition, promising LTCC materials with stable temperature characteristics and co-firing compatibility with silver electrodes can be obtained in the nominal Zn(Mn 1À x Ti x) 3 O 7 (x¼0.68) ceramics with 5 wt% ZnO-B 2 O 3 glass sintered at 900 1C. This material possesses the following microwave dielectric properties: ε r of 18.2, Q Â f of 12,018 GHz, and τ f of À3.98 ppm/1C.

Low-temperature co-fired ceramics (LTCCs), with a Zn(Mn 1 À x Ti x) 3 O 7 (0rxr1.0) composition, were prepared using a conventional solid-state method. A novel ZnMn 3 O 7 ceramic was obtained, with a ZnMn 2 O 4 spinel structure, ε r of 7.32, Q Â f of 13,667 GHz, and τ f of À58.33 ppm/1C. The effect of various dopant concentrations on the microstructure and microwave dielectric properties of the material was investigated. Results showed that the increase in dopant concentration changed the phase composition, improved the microwave dielectric properties, and reduced the sintering temperature of the Zn(Mn 1 À x Ti x) 3 O 7 by a factor of 250 1C. The dielectric constant of Zn(Mn 1À x Ti x) 3 O 7 varied from 7.32 to 33.08 at x¼0.8. However, the maximum value was reduced to 27.67 at x¼ 1.0. Moreover, the value of Q Â f increased significantly up to a maximum value of 18,934 GHz, whereas τ f changed gradually from À58.33 ppm/1C to þ289.25 ppm/1C. In addition, promising LTCC materials with stable temperature characteristics and co-firing compatibility with silver electrodes can be obtained in the nominal Zn(Mn 1À x Ti x) 3 O 7 (x¼0.68) ceramics with 5 wt% ZnO-B 2 O 3 glass sintered at 900 1C. This material possesses the following microwave dielectric properties: ε r of 18.2, Q Â f of 12,018 GHz, and τ f of À3.98 ppm/1C.