Microwave dielectric properties of Ba_3.75Nd_9.5Ti_18−zCr_4z/3O₅₄ ceramics

The Ba_3.75Nd_9.5Ti_18−z Cr_4z/3O₅₄ (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 Ba_3.75Nd_9.5Ti_18−z Cr_4z/3O₅₄ (BNTCz) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that pure BaNd₂Ti₅O₁₄ phase with tungsten bronze structure existed for z ≤ 1, but the secondary phase Ba₄Ti₁₂O₂₇ 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 _r ) 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 _f ) 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 _r  = 81.53, Q×f = 11,294 GHz and τ _f  = + 39.2 ppm/°C were obtained as z = 0.5 sintered at 1420 °C for 2 h.