Structural and electrical characterization of CeAlO₃ ceramics

The crystal structure and electrical properties of CeAlO₃ ceramics prepared by the mixed oxide route have been investigated. X-ray and electron diffraction data show the room temperature structure to be described by the tetragonal I4/mcm space group [a=5.3253(5) Å and c =7.5860(9) Å; Z=4, and theoretical density, D_x=6.64 g/cm³]. CeAlO₃ ceramics sintered at 1500 °C under flowing 5%H ₂-95%N₂ gas for 4 h reach ∼94% of D_x with a microstructure of randomly distributed equiaxed grains of average grain size ∼2 μm. Conventional transmission electron microscopy reveals needle-shaped ferroelastic domains in some grains. The relative permittivity ε_r of CeAlO₃ ceramics is ∼18-20 in the range of ∼10-300 K. At room temperature and microwave frequencies, CeAlO3 ceramics exhibit ε_r∼20.7,Qf_r∼40 117 GHz (at 9.5 GHz), and T_f∼ -57 ppm/K. The ion polarizability for Ce³⁺ is calculated to be 4.46 ų. Revised dielectric polarizabilities for rare-earth lanthanides are also presented.