摘要
Ceramic samples of(Bi_(1-x)Pb_(x))NbO_(4)(x=0,0.025,0.05,0.10,0.15,0.20)with 0.75 wt.%V2O5 addition sintered at 920℃,940℃ and 960℃ are investigated.Pb is selected as a substitute for Bi^(3+)in BiNbO_(4) ceramics as it exists in two stable valence states of+2 and+4 and the average valency matches to that of Bi^(3+).The average Shannon radius(for octahedral coordination)of Pb^(2+)(1.19Å)and Pb^(4+)(0.775Å)cations is 0.9825Å,which is similar to that of Bi^(3+)ion(1.03Å).The dense(>94%)polycrystalline(Bi_(1-x)Pb_(x))NbO_(4) samples fabricated mostly reveal orthorhombic(Pnna)phase(α-BiNbO_(4),Sp.Gp.52)by powder XRD.Presence of satellite Pb2Nb2O7 phase,the amount of which is increasing with increase in Pb content,is also noticed.The microwave dielectric constant(ε'r)values of the niobates are found to increase from 42 to 71,whereas the quality factor(Qu.f)values are found to decrease from 5400 to 550 GHz with increasing substitution of Pb.The compositions so synthesized are important as hardly there are any microwave dielectric ceramics available with 45<ε'r<75.
