Thin films were fabricated via metalorganic decomposition methods with three compositions: Bi1.5Zn1.0Nb1.5O7, Bi1.5Zn0.5Nb1.5O6.5, and Bi2Zn2/3Nb4/3O7. The Bi1.5Zn0.5Nb1.5O6.5 composition is a low temperature phase with the cubic pyrochlore structure. This phase may undergo a peritectoid decomposition at 700 °C to the high temperature phases of Bi1.5Zn1.0Nb1.5O7 and BiNbO4. Both the Bi1.5Zn1.0Nb1.5O7 and Bi1.5Zn0.5Nb1.5O6.5 cubic pyrochlores show medium room temperature permittivities (150 and 180, respectively) with negative temperature coefficients of capacitance and a low temperature dielectric relaxation. Both Bi1.5Zn1.0Nb1.5O7 and Bi1.5Zn0.5Nb1.5O6.5 films showed substantial dielectric tunability with electric field (>30%). The field dependence of the dielectric permittivity of the zirconolite structured Bi2Zn2/3Nb4/3O7 thin films demonstrates an unusual field induced transition at high field ∼2 MV/cm, with a maximum tunability of 20%. It is hypothesized that this is associated with field forced ordering of the Zn atoms between two closely spaced, partially occupied sites.

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Bismuth pyrochlore ceramics have modest temperature coefficients of capacitance, good microwave properties, and can be prepared at relatively modest temperatures (∼900 – 1100 °C). This work focuses on the preparation and characterization of thin films in this family for the first time. A sol-gel procedure using bismuth acetate in acetic acid and pyridine, in combination with zinc acetate dihydrate and niobium ethoxide in 2-methoxyethanol was developed. The solution chemistry was adjusted to prepare (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 and Bi2(Zn1/3Nb2/3)2O7 films. Solutions were spin-coated onto platinized Si substrates and crystallized by rapid thermal annealing. In both cases, crystallization occurred by 550 °C into the cubic pyrochlore structure. (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films remained in the cubic phase up to crystallization temperatures of 750 °C, while the structure of the Bi2(Zn1/3Nb2/3)2O7 thin films is dependent of the firing temperature: cubic below 650 °C and orthorhombic above 750 °C. A mixture of cubic and orthorhombic structures is found at 700 °C. The resulting BZN films are dense, uniform, and smooth (rms roughness of < 5 nm). Cubic bismuth zinc niobate films show dielectric constants up to 150, a negative temperature coefficient of capacitance, TCC, (∼ - 400 ppm/°C), tan δ < 0.01, and a field tunable dielectric constant. Orthorhombic films showed smaller dielectric constants (∼80), low tan δ (< 0.01), positive TCC, and field independent dielectric constants. TCC could be adjusted to new 0 ppm/°C using a mixture of orthorhombic and cubic material.

Densification was observed when bulk ceramic superconductors with a composition of Bi 1.8 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10؉␦ were sintered for short times (<4 h) near the incongruent melting temperature. The initial shrinkage of the powder compacts was correlated with the existence of a transient liquid phase. Retrograde densification, which is a decrease in density, occurred for longer sintering times and was attributed to changes in pore structure. The results provide direction for future processing of bulk bismuth-based superconductors and powder-in-tube tapes for the fabrication of long-length wire.