Study of the microwave dielectric properties of (La_1−xSm_x)NbO₄ (x=0‐0.10) ceramics via bond valence and packing fraction

Abstract

The (La1−xSmx)NbO4 (x=0‐0.10) ceramics were prepared by the conventional solid‐state reaction method. The microstructure and the microwave dielectric properties were discussed in detail. The X‐ray diffraction patterns of (La1−xSmx)NbO4 (x=0‐0.10) showed that only a single monoclinic fergusonite structure of LaNbO4 could be found. The dielectric constant (εr) was affected by the dielectric polarizabilities and the B‐site bond valence. The variation trend of Q×f0 was in accordance with packing fraction. The temperature coefficient of resonant frequency (τf) had a close relationship with the B‐site bond valence, which was determined by the bond strength and bond length. When sintered at 1325°C for 4 hours, the (La1−xSmx)NbO4 ceramics with x=0.08 exhibited enhanced microwave dielectric properties: εr=19.37, Q×f0=62203 GHz and τf=2.57 ppm/°C. In addition, we made an overview about the ceramics that possess the same packing fraction and bond valence relationships, the results show that this structure‐property relationship has a wide applicability.

Structure and microwave dielectric characteristics of Sr2[Ti1−x(Al0.5Nb0.5)x]O4 (x ≤ 0.50) ceramics

“…With further increasing x , the Qf starts decreasing to 83 960 and 77 580 GHz at x = 0.30 and 0.50, respectively. This has been already correlated with the decreasing trend of packing fraction …”

“…This has been already correlated with the decreasing trend of packing fraction. 26,34 Some typical microwave dielectric ceramics with the dielectric constant close to the present ones are summarized in Table 6. The present ceramics, without noble element such as Ta, indicate the excellent microwave dielectric characteristics which are almost comparable with those of Ba(Zn 1/3 Ta 2/3 )O 3 and Ba(Mg 1/3 Ta 2/3 )O 3 and obviously better than other materials previously reported.…”

“…The synchronized variation tendency of the respected values of ε r , α Theo. (Å 3 ), and ε r calc can be attributed to the lack of rattling effect in the bond characteristics of oxygen octahedron, 14,26 which is explained in later section.…”

A low-firing melilite ceramic Ba2CuGe2O7 and compositional modulation on microwave dielectric properties through Mg substitution

“…The intrinsic influence on quality factor can be reflected by the packing fraction, as empirically summarized by Kim et al [29,30]. For a certain material system, the higher of the packing fraction, the smaller space for the thermal motion of cations or anions, thus leading to lower dielectric losses [31]. The packing fraction is defined as the total volume of packed ions over the volume of the unit cell and the calculated values are shown in Fig.…”

A low-firing melilite ceramic Ba2CuGe2O7 and compositional modulation on microwave dielectric properties through Mg substitution

“…Theoretically, the dielectric permittivity is inherently affected by the molecular polarizability ( The intrinsic influence on quality factor can be reflected by the packing fraction, as empirically summarized by Kim et al [29,30]. For a certain material system, the higher of the packing fraction, the smaller space for the thermal motion of cations or anions, thus leading to lower dielectric losses [31]. The packing fraction is defined as the total volume of packed ions over the volume of the unit cell and the calculated values are shown in Figure 9d.…”