Crystal Chemistry and Dielectric Properties of Chemically Substituted (Bi 1.5 Zn 1.0 Nb 1.5 )O 7 and Bi 2 (Zn 2/3 Nb 4/3 )O 7 Pyrochlores

The effect of the chemical substitution of Ti, Zr, and Gd cations on the structure and properties of bismuth‐based pyrochlores was investigated for (Bi 1.5 Zn 1.0 Nb 1.5 )O 7 and Bi 2 (Zn 2/3 Nb 4/3 )O 7 . Broad ranges of solid solutions based on cubic (Bi 1.5 Zn 1.0 Nb 1.5 )O 7 were observed for Ti and Zr cations: (Bi 1.5 Zn 1−( x /3) Nb 1.5−(2 x /3) Zr x )O 7 (0.0 ≤ x ≤ 1.5) and (Bi 1.5 Zn 1−( x /3) Nb 1.5−(2 x /3) Ti x )O 7 (0.0 ≤ x ≤ 2.25). For Gd cations, the range of solid solution was quite limited in (Bi 1.5− x Gd x Zn 1.0 Nb 1.5 )O 7 (0.0 ≤ x ≤ 0.2); however, the range of solid solution is more extensive in the system that contains Ti and Gd cations ((Bi 1.5− x Gd x Zn 0.5 Ti 1.5 Nb 0.5 )O 7 (0.0 ≤ x ≤ 0.6)). The stability fields of the solid solutions could be interpreted by using the ratio of the ionic sizes of the A‐ and B‐site ions in the pyrochlore structure ( R A / R B ). The substituted phases exhibited permittivities (κ′) in the range of ∼100–200 and relatively low dielectric losses (tan δ < 7 × 10 −4 ) at 1 MHz. The temperature coefficients of permittivity (τ κ ) varied in accordance with the R A / R B value and could be tuned from −88 ppm/K to −1300 ppm/K. For the orthorhombic Bi 2 (Zn 2/3 Nb 4/3 )O 7 pyrochlore, the ranges of solid solution were very limited and the dielectric properties remained similar to those of the undoped phase (κ′= 90, τ κ = 150 ppm/K).