Negative Thermal Expansion Change Of Different Stoichiometric Proportions Calcium-doped Strontium Barium Niobate Crystals

摘要

The polarization Raman spectra were measured for the calcium-doped strontium barium niobate crystals ((Ca_(0.28)Ba_(0.75))×(Sr_(0.60)Ba_(0.40))_(1-x)Nb_2O_6 (x = 0.25,0.50 or 0.75, CSBN) to determine the negative thermal expansion(NTE) change induced by different stoichiometric proportions calcium-doped concentration. The different count-intensity (CI) of Raman peaks with the scattering geometry Z(XY)Z, corresponding to the symmetry species B_2, are attributed to the different vacancy rate(VR) in A2 sites of tetragonal tungsten bronze-type structure, which can result in the change of the short-range molecular force (SRMF) between ions filled in A2 sites and Nb-O octahedron. Since the thermal properties of materials direct responding to the vibration of crystal lattices, the NTE change of CSBN crystals are considered as arising due to the geometry change for the different calcium-doped concentration.