Structure and Microwave Dielectric Properties of Low Firing <scp> <scp>Bi</scp> </scp> ₂ <scp> <scp>Te</scp> </scp> ₂ <scp> <scp>W</scp> </scp> ₃ <scp> <scp>O</scp> </scp> ₁₆ Ceramics

Abstract

Dense Bi 2 Te 2 W 3 O 16 ceramics were prepared by the conventional solid‐state reaction route. X ‐ray diffraction data show the room‐temperature ( RT ) crystal symmetry of Bi 2 Te 2 W 3 O 16 to be well described by the centrosymmetric monoclinic C 2 /c space group [ a = 21.280(5) Å, b = 5.5663(16) Å, c = 12.831(3) Å and β = 124.014(19)° and Z = 4]. Raman spectroscopy analyses are in broad agreement with space group assignment, but also revealed the presence of Bi 2 W 2 O 9 as a secondary phase. This phase is present as plate‐like grains embedded on a fine‐grained equiaxed matrix, as revealed by scanning electron microscopy. From the fitting of infrared reflectivity data the relative permittivity, ε r , was estimated as 34.2, and the intrinsic quality factor, Q u × f as 57 500 GHz. At RT and microwave frequencies, Bi 2 Te 2 W 3 O 16 ceramics sintered at 720°C for 6 h exhibit ε r ~ 34.5, Q u × f = 3173 GHz (at 7.5 GHz), and temperature coefficient of resonant frequency, τ f = −92 ppm/°C. This shows a good agreement between the estimated and measured ε r values, but also shows that, in principle, the dielectric losses of the ceramics are of extrinsic origin.