A series of the twinned 8H hexagonal perovskites in the Ba 4 LiNb 3Àx Ta x O 12 (x 5 0-3) system were synthesized by the conventional solid-state reaction method. Ba 4 LiNb 3Àx Ta x O 12 solid solutions were single phase in the whole range of x values. The ceramics exhibit perfect microwave dielectric properties with relative permittivity, e r B28-37, high quality factor, Q Â fB37 000-104 000 GHz, and temperature coefficient of resonant frequency, s f B125-165 ppm/1C.

The tetragonal tungsten bronze (TTB)‐structured Ba4Sm2Fe2M8O30 (M=Nb, Ta) dielectrics were prepared and investigated. Dielectric and ferroelectric behaviors revealed that the niobate and the tantalate display ferroelectric and paraelectric nature at room temperature (RT), respectively. The dielectric spectrum showed that Ba4Sm2Fe2Ta8O30 ceramic has a high dielectric constant (∼97), a comparatively low temperature coefficient of dielectric constant (∼−105 ppm/°C), and a low dielectric loss (∼10−3) (at 1 MHz). These results indicated that the present tantalate might be a new temperature‐compensating ceramic.

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The dielectric ceramics Ba4Pr2Fe2Ta8O30 and Ba4Eu2Fe2Ta8O30 with a tetragonal tungsten bronze structure were synthesized and characterized. Dielectric and ferroelectric behaviors indicated that the ceramics are paraelectric above room temperature. Dielectric measurement showed that the present ceramics have high‐temperature stability, a comparatively low temperature coefficient of dielectric constant (τɛ) of −30 and −63 ppm/°C, with a high dielectric constant (ɛr) of 110 and 87.6 together with a low dielectric loss (tan δ) of 0.0010 and 0.0012 (at 1 MHz) for Ba4Pr2Fe2Ta8O30 and Ba4Eu2Fe2Ta8O30, respectively. These results indicated that the Ba4Ln2Fe2Ta8O30 (Ln=Pr, Eu) ceramics might be promising in temperature‐stable multilayer ceramic capacitors.