Structural, Spectral, Dielectric, and Microwave Absorption Properties of Gd–Cr-Doped BiFeO3 Materials for High-Frequency Applications

Nanocrystalline Bi_1−xGd_xFe_1−xCr_xO₃ (x = 0.00, 0.04, 0.08, 0.12, 0.16) samples were fabricated via sol–gel autocombustion. x-Ray diffraction analysis (XRD) confirmed a single-phase rhombohedral structure. Crystallite size ranged from 30 nm to 25 nm, emphasizing their nanoscale characteristics. The lower bulk density compared with the x-ray density indicated the presence of pores. Lattice constants were computed with Cell software, indicating that substituting Bi³⁺ with the smaller Gd³⁺ ions resulted in modifications to the lattice structure. Fourier-transform infrared (FTIR) spectra revealed absorption bands between 400 cm⁻¹ and 600 cm⁻¹, with shifts observed as the Gd concentration increased, signifying doping effects on the structure. A decrease in the frequencies of both ν₁ and ν₂ bands was observed, attributed to the disruption of the Fe³⁺–O²⁻ bond and the rearrangement of cations due to Gd incorporation. Dielectric studies performed at room temperature within the 1–3 GHz range revealed a decrease in both real and imaginary parts of permittivity as frequency increased, consistent with the Maxwell–Wagner polarization model. At higher frequencies, the alternating-current (AC) conductivity increases substantially owing to the contribution of grains and enhanced polarization at neighboring sites. The sample with x = 0.16 exhibited low dielectric losses of 0.21 GHz at 3 GHz. The decrease in the quality factor is linked to a rise in loss caused by the formation of pores within the grains. Moreover, for x = 0.16, a reflection loss of −66.57 dB was measured at 0.98 GHz. These findings highlight the potential of these materials for cutting-edge uses, especially in multilayer chip inductors and high-frequency microwave systems.