Enhanced Microwave Resonance Properties of Pseudo-Tungsten-Bronze Ba_6-3xR_8+2xTi₁₈O₅₄ (R = Rare Earth) Solid Solutions Explained by Electron–Phonon Interaction

Microwave dielectrics consisting of pseudo-tungsten-bronze solid solutions form compositional ordering at x = 2/3 with the Ba_6-3xR_8+2xTi₁₈O₅₄ (R = La, Nd, Pr, Sm, Eu, and Gd) formula. The Qf value of the x = 2/3 composition shows the highest value for Sm, but a discontinuity at Eu. When doping with heavier rare earth species, the crystal structure becomes unstable and needs stabilization with Nd. In this paper, we suggest for the first time that the electron–phonon interaction is responsible for this phenomenon. As the unit cells without Ba ions in the perovskite blocks caused tensile stress, the dielectric constant and dielectric losses increase by means of the ionic size of the dopant in the octahedral sites, but only when elements with a low electron–phonon interaction are used.