Temperature independent low loss dielectrics based on quaternary pyrochlore oxides

Quaternary pyrochlore phases of the general formula Bi2-xCaxM2-yM'O-y(7-x/2+y/2) (M = Ti, Hf, Sn; M' = Sb, Nb, Ta) were prepared by solid state reactions and characterized via structural and dielectric properties. The cubic a lattice parameters show an expected linear relationship with the ionic radii of the substituted M cations. The solid solution Bi2-xCaxSn2-ySbyO7-x/2+y/2 was analyzed by X-ray and neutron diffractions. The solubility limit is close to x = 1.3, and for x > 1.3, the reaction products contain a mixture of the pyrochlore phase and the Ca2Sb2O7 weberite phase. The refined formulas for compositions with nominal calcium content x = 0.5, 1.0, and 1.5 are Bi1.36Ca0.64Sn1.60Sb0.40O6.88, Bi0.82Ca1.18Sn1.10Sb0.90O6.86, and Bi0.76Ca1.24Sn1.06Sb0.94O6.85 respectively, indicating slight oxygen deficiencies. Temperature and frequency independent dielectric constants and low loss are observed at 1 MHz. The dielectric constants vary from 16 to 98 depending on the composition. We have also prepared new cubic quaternary pyrochlores with the formula BiCdMTeO7, where M = Al, Cr, Ga, In, Fe, Mn, and Sc. Magnetic property measurement shows paramagnetism in the M = Cr and Mn phases but antiferromagnetism with short-range correlations in the M = Fe phase. All these compositions are insulating. The measured dielectric constants and dielectric loss are independent of temperature and frequency.