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

Novel Ba 2 RE 2 Si 4 O 13 ( RE = La, Nd, Sm, Eu, Gd, Ho, Er and Yb) ceramics were prepared by traditional solid reaction methods. The phase compositions of Ba 2 RE 2 Si 4 O 13 ceramics were explored. The triclinic structure with P 1 ¯ space group of Ba 2 RE 2 Si 4 O 13 ceramics was confirmed by TEM and Rietveld refinement analyses, and the decrease in the ionic radius of RE 3+ induced the phase transition from low symmetry (triclinic) to high symmetry (monoclinic) between Ba 2 Sm 2 Si 4 O 13 and Ba 2 Eu 2 Si 4 O 13 . ε r-exp of the Ba 2 RE 2 Si 4 O 13 ceramics was significantly affected by ionic polarisability. The ‘rattling and compressing effects’ of cations also affected the ε r-exp of Ba 2 RE 2 Si 4 O 13 ceramics. The intrinsic dielectric loss of Ba 2 RE 2 Si 4 O 13 ceramics were evaluated by the far-IR reflectivity spectrum, and high Q × f values of the Ba 2 Nd 2 Si 4 O 13 and Ba 2 Eu 2 Si 4 O 13 ceramics were attributed to their large total lattice energy and activation energy. The average bond valence of RE 3+ played an important role in controlling the τ f values of the Ba 2 RE 2 Si 4 O 13 single-phase ceramics, and the high average bond valence of RE 3+ corresponded with the small negative τ f values. Great microwave dielectric properties ( ε r = 11.52, Q × f = 33,600 GHz at 11.80 GHz and τ f = ‒25.6 ppm/ °C) were obtained in the Ba 2 Nd 2 Si 4 O 13 single-phase ceramic.