Sintering behavior, structural phase transition, and microwave dielectric properties of La_1‐xZn_xTiNbO_6‐x/2 ceramics

Abstract

La1‐xZnxTiNbO6‐x/2 (LZTN‐x) ceramics were prepared via a conventional solid‐state reaction route. The phase, microstructure, sintering behavior, and microwave dielectric properties have been systematically studied. The substitution of a small amount of Zn2+ for La3+ was found to effectively promote the sintering process of LTN ceramics. The corresponding sintering mechanism was believed to result from the formation of the lattice distortion and oxygen vacancies by means of comparative studies on La‐deficient LTN ceramics and 0.5 mol% ZnO added LTN ceramics (LTN+0.005ZnO). The resultant microwave dielectric properties of LTN ceramics were closely correlated with the sample density, compositions, and especially with the phase structure at room temperature which depended on the orthorhombic‐monoclinic phase transition temperature and the sintering temperature. A single orthorhombic LZTN‐0.03 ceramic sintered at 1200°C was achieved with good microwave dielectric properties of εr~63, Q×f~9600 GHz (@4.77 GHz) and τf ~105 ppm/°C. By comparison, a relatively high Q × f~80995 GHz (@7.40 GHz) together with εr~23, and τf ~−56 ppm/°C was obtained in monoclinic LTN+0.005ZnO ceramics sintered at 1350°C.

Octahedral distortion, phase structural stability, and microwave dielectric properties in equivalently substituted LaTiNbO6 ceramics

“…The above‐mentioned phase structural evolution could be also reflected by the variation in the corresponding grain morphology, as shown in Figure . It can be seen that the x =0.01 and x =0.2 samples owned polygonal and short rod‐like grain morphologies, respectively, which are typical of M and O‐phase LaTiNbO 6 ceramics . This observation well agreed with the XRD results in Figure A.…”

“…The substitution of Ce or Sm at A‐sites of LaTiNbO 6 was reported to induce an M–O phase transition, accompanying tunable microwave dielectric properties . In addition, a single O‐phase ceramic could be also achieved by an annealing process or by lowering the sintering temperature via Zn 2+ substitution . Actually, both M and O aeschynite consist of identical double‐octahedron structure units (Ti,Nb) 2 O 10 , but these units connect in different ways, i.e.…”

Fabrication of near‐infrared transparent Dy2Zr2O7 ceramic by controlled pre‐calcination of powders

“…The small amount of Dy 2 Zr 2 O 7 (2–8 mol%) produced during pre‐calcining may become the seed for sintering, and the oxygen vacancies generated by the doping of Dy 3+ into ZrO 2 will be in favor of oxygen motion during sintering. Substitution of Zr 4+ (ion radius: .72 Å) by Dy 3+ (ion radius: .912 Å) will also cause the lattice distortion resulting in a reduction of the diffusion activation energy, and the acceleration of the ion mobility, thus promoting the densification of ceramics during sintering 9,30,31 . However, pores would be readily closed before elimination when the migration velocity of the grain boundary is faster than that of pores in the initial sintering stage, uniform and appropriate grain growth in sintering are favorable to the expulsion of pores 32 …”

“…Substitution of Zr 4+ (ion radius: .72 Å) by Dy 3+ (ion radius: .912 Å) will also cause the lattice distortion resulting in a reduction of the diffusion activation energy, and the acceleration of the ion mobility, thus promoting the densification of ceramics during sintering. 9,30,31 However, pores would be readily closed before elimination when the migration velocity of the grain boundary is faster than that of pores in the initial sintering stage, uniform and appropriate grain growth in sintering are favorable to the expulsion of pores. 32 As seen in Figures 1D and 2, the APS of the raw materials and that of the pre-calcined at different temperatures increased from around 200 to about 450 nm, and the powders calcined at 1200 and 1250 • C demonstrate good particle dispersion and size uniformity, which is more beneficial to sintering.…”