Effects of Ni2+ substitution on the crystal structure, bond valence, and microwave dielectric properties of BaAl2-2xNi2xSi2O8-x ceramics

摘要

BaAl2-2xNi2xSi2O8-x (x = 0, 0.005, 0.01, 0.02, 0.03) ceramics were prepared using traditional solid phase reaction method. The microwave dielectric properties, including permittivity (epsilon(r)), quality factor (Q x f), and temperature coefficient of resonant frequency (tau(f)), were discussed based on the bond valence theory. The firstprinciple calculation was adopted to determine the site (Ba, Al, and Si) where doping element (Ni2+) would be inclined to occupy. The substitution of Ni2+ for Al3+ contributed to the breaking of Al-O and Si-O bonds and then facilitated the BaAl2Si2O8 (BAS) hexacelsian-celsian transformation. Moreover, this substitution could change the bond strength between cation and oxygen anion due to the variation of the bond valence, which reasonably explained the variation of epsilon(r), Q x f, and tau(f) values. Well-sintered and completely transformed celsian ceramics can be obtained after doping with Ni2+. When x = 0.01, compact BaAl1.98Ni0.02Si2O7.99 ceramic exhibited highly promising microwave dielectric properties: epsilon(r) = 6.89, Q x f = 53, 287 GHz and tau(f) = -25.31 x 10(-6)/degrees C.