Polycrystalline samples of Sr₂Ni_1−xMg_xWO₆ (x = 0.00, 0.02, 0.04, and 0.06) were prepared through a solid-state reaction method and the crystal structure, optical and dielectric properties of the samples were studied using X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS) respectively. Rietveld analysis of XRD patterns confirmed that the compounds crystallized in a tetragonal structure with a space group I4/m. The analysis revealed that the unit cell volume of the samples increased from 245.092 ų to 245.273 ų due to the larger ionic radius of Mg²⁺ (0.72 Å) compared to that of Ni²⁺ (0.69 Å). UV-vis analysis revealed that the band gap energy of the samples decreased from 3.30 eV to 3.24 eV as the doping amount increased from x = 0.00 to x = 0.06. This occurrence was attributed to the large size of Mg²⁺ that reduced the excitation distance for the valence electrons. FTIR analysis was performed for all samples and the characteristic absorption bands W–O₆ confirmed the double perovskite structure. A dielectric characterization study using electrochemical impedance spectroscopy (EIS) revealed that the dielectric constant (ε′) and dielectric loss (ε′′) were higher in the low frequency area below 0.01 Hz and decreased upon increasing the frequency above 0.01 Hz until they reached a constant value at 1 MHz. At low frequency, the compound with Mg = 0.06 exhibited the highest value which was approximately 280. In addition, this compound showed the least dielectric loss at 0.01 Hz.

中文翻译：

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Sr2Ni1−xMgxWO6 (x = 0.00、0.02、0.04 和 0.06) 双钙钛矿的结构、光学和介电特性

Sr ₂ Ni _{1− x} Mg _x WO ₆ ( x = 0.00、0.02、0.04和0.06)的多晶样品是通过固态反应方法制备的，并使用X研究了样品的晶体结构、光学和介电性能分别为-射线衍射（XRD）、紫外-可见漫反射光谱（UV-vis）、傅里叶变换红外光谱（FTIR）和电化学阻抗谱（EIS）。XRD 谱的 Rietveld 分析证实化合物以四方结构结晶，空间群为I 4/ m。分析表明，样品的晶胞体积从 245.092 Å ³增加由于 Mg ²⁺ (0.72 Å) 的离子半径比 Ni ²⁺ (0.69 Å) 的离子半径更大，因此达到 245.273 Å ³。UV-vis 分析表明，随着掺杂量从x = 0.00 增加到x = 0.06 ，样品的带隙能量从 3.30 eV 降低到 3.24 eV 。这种情况的发生归因于 Mg ²⁺的大尺寸，这减少了价电子的激发距离。对所有样品进行了 FTIR 分析，特征吸收带 W-O ₆证实了双钙钛矿结构。使用电化学阻抗谱 (EIS) 进行的介电表征研究表明，介电常数 ( ε') 和介电损耗 ( ε '') 在低于 0.01 Hz 的低频区域较高，并随着频率增加到 0.01 Hz 以上而降低，直到它们在 1 MHz 达到恒定值。在低频下，Mg = 0.06 的化合物表现出最高值，约为 280。此外，该化合物在 0.01 Hz 下表现出最小的介电损耗。