Investigations of crystal structure, phase compositions and intrinsic dielectric properties of novel Ba2RE2Si4O13 ceramics by bond theory and infrared spectroscopy

Abstract

Novel Ba2RE2Si4O13 (RE = La, Nd, Sm, Eu, Gd, Ho, Er and Yb) ceramics were prepared by traditional solid reaction methods. The phase compositions of Ba2RE2Si4O13 ceramics were explored. The triclinic structure with P1¯ space group of Ba2RE2Si4O13 ceramics was confirmed by TEM and Rietveld refinement analyses, and the decrease in the ionic radius of RE3+ induced the phase transition from low symmetry (triclinic) to high symmetry (monoclinic) between Ba2Sm2Si4O13 and Ba2Eu2Si4O13. εr-exp of the Ba2RE2Si4O13 ceramics was significantly affected by ionic polarisability. The ‘rattling and compressing effects’ of cations also affected the εr-exp of Ba2RE2Si4O13 ceramics. The intrinsic dielectric loss of Ba2RE2Si4O13 ceramics were evaluated by the far-IR reflectivity spectrum, and high Q × f values of the Ba2Nd2Si4O13 and Ba2Eu2Si4O13 ceramics were attributed to their large total lattice energy and activation energy. The average bond valence of RE3+ played an important role in controlling the τf values of the Ba2RE2Si4O13 single-phase ceramics, and the high average bond valence of RE3+ corresponded with the small negative τf values. Great microwave dielectric properties (εr = 11.52, Q × f = 33,600 GHz at 11.80 GHz and τf = ‒25.6 ppm/ °C) were obtained in the Ba2Nd2Si4O13 single-phase ceramic.