Novel microwave dielectric LTCCs based uponV2O5 doped M2+Cu2Nb2O8 compounds (M2+ = Zn, Co, Ni, Mg and Ca)

The copper-niobates, M2+Cu2Nb2O8 (M2+ = Zn, Co, Ni, Mg or Ca) have good microwave dielectric properties when sintered between 985–1010 °C and 1110 °C for CaCu2Nb2O8. Therefore, they would be potential dielectric LTCC materials if they could be made to sinter below 960 °C (melting point of silver). To this end, additions of 3 wt.% V2O5 were made to ZnCu2Nb2O8, CoCu2Nb2O8, NiCu2Nb2O8, MgCu2Nb2O8 and CaCu2Nb2O8, and their sintering and dielectric behaviour was investigated for samples fired between 800 and 950 °C. Doping lowered sintering temperatures to below the 960 °C limit in all cases. Doping had the general effect of reducing ɛr, density, Qf and τf, although doped CaCu2Nb2O8 had a Qf value of 9300 GHz, nearly four times that of the best undoped sample. Doped ZnCu2Nb2O8 fired to 935 °C had Qf = 10,200 GHz, and for doped CoCu2Nb2O8 fired to 885 °C Qf = 7500 GHz. When doped and undoped samples all fired to 935 °C were compared, all doped samples had greater ɛr and density, and all except ZnCu2Nb2O8 had a smaller τf. All doped samples had a more linear relationship between frequency and temperature in the range 250–300 K.