Crystal Structure and Ferroelectric Evidence of BaZnSi₃O₈, a Low‐Permittivity Microwave Dielectric Ceramic

Abstract

BaZnSi3O8 ceramic was prepared by the conventional solid‐state method and sintered at 1100 °C. XRD and synchrotron Rietveld refinement analyses revealed the BaZnSi3O8 ceramic presented a monoclinic structure with a space group of P21/a (No.14), which is reported for the first time. The BaZnSi3O8 ceramic presented a weak ferroelectricity, which was confirmed by the P–E loop and the 90° nanoscale ferroelectric domain. Although ϵr–T displayed two ϵr abnormal peaks at 400 °C and 460 °C, the Curie temperature (Tc) was located at 460 °C according to the dielectric loss and Curie–Weiss law. Moreover, the BaZnSi3O8 ceramic exhibited optimized microwave dielectric properties with ϵr=6.55, Q×f=52400 GHz, and τf=−24.5 ppm/°C. Hence, the BaZnSi3O8 ceramic in the ternary BaO‐ZnO‐SiO2 system possessed both weak ferroelectricity and microwave dielectric properties. These results are expected to break the technical barrier of ferroelectric phase shifter applications in microwave and even millimeter‐wave frequency bands.

Optimized crystal structure and microwave dielectric properties of BaZnSi3O8‐based ceramics

“…As shown in Figure 5, All the tetrahedra are uniformly distributed diagonally in the unit cell, wherein each [SiO 4 ] tetrahedron is connected to one [ZnO 4 ] tetrahedron and the other three [SiO 4 ] tetrahedra. The Zn 2+ and Si 4+ spaces are relatively independent and occupy 1/4 and 3/4 of the coordination sites 12 . The nontetrahedral positions are occupied by Ba 2+ , which are arranged parallel to the (0 1 0) plane.…”

“…The Zn 2+ and Si 4+ spaces are relatively independent and occupy 1/4 and 3/4 of the coordination sites. 12 The nontetrahedral positions are occupied by Ba 2+ , which are arranged parallel to the (0 1 0) plane.…”

“…Figure 1 shows the phase diagram of BaO-ZnO-SiO 2 , 7 During the process of synthesizing BaAl 2-2x (ZnSi) x Si 2 O 8 , Song 11 discovered that BaZnSi 3 O 8 exhibits a new single-phase structure when x = 1. As a new material with promising application prospects, The crystal structure of and X-ray diffraction pattern of BaZnSi 3 O 8 ceramic as a new material was first reported by Zou 12 in 2021. According to him, BaZnSi 3 O 8 rarely combines weak ferroelectricity and microwave dielectric properties.…”

Crystal structure and enhanced microwave dielectric properties of the Ce2[Zr1−x(Al1/2Ta1/2)x]3(MoO4)9 ceramics at microwave frequency

“…In recent years, Mo-based microwave dielectric ceramics were studied in depth, as shown in Fig. 8 [10,[17][18][19][20][21][26][27][28][29][30][31][32] In general, the microwave dielectric properties are associated with the extrinsic factors. The extrinsic factors include grain boundaries, pores, abnormal grains, defect, and dislocation, which are the main factors that produce the dielectric loss.…”

“…Densification and a relatively uniform microstructure are the main reasons for optimizing the quality factor; the decline of Q × f values at a higher sintering temperature can be attributed to intrinsic loss[24,25].In recent years, Mo-based microwave dielectric ceramics were studied in depth, as shown in Fig. 8[10,[17][18][19][20][21][26][27][28][29][30][31][32]. Most Mo-based microwave dielectric ceramics have Q × f in the range of 20,000-80,000 GHz.…”