High-frequency response in Sr1−xCaxTiO3 powders studied by terahertz time-domain spectroscopy

Strontium Calcium titanate (SCT) Sr1−xCaxTiO3 nanopowders have been successfully synthesized by sol–gel method. The effect of Ca2+ ion content from 0 to 1 on their crystal structure, microstructure, transmission and dielectric properties in terahertz range was systematically investigated. The results revealed that single SCT phases with well crystallinity were formed at 900 °C for 2 h. The grain size of the SCT powders was decreased by increasing the Ca2+ ion molar ratios. X-ray diffraction (XRD) and Raman spectra measurement results demonstrated that obvious reduction of symmetry and Raman modes related to structural information varied with the Ca2+ ion composition x. The sequence of SCT phase transitions with increasing Ca content is from cubic through tetragonal I4/mcm to orthorhombic Pbnm. The THz transmission of SCT revealed by terahertz time-domain spectroscopy was changed by varying the Ca2+ ion composition. Meanwhile, the time lag between reference and the SCT could be adjusted between around 20 ps and 30 ps, which increased with increased Ca content. The permittivity of stressed Sr1−xCaxTiO3 powders was obtained by terahertz time-domain spectroscopy. These results revealed that the Ca2+ ion in SCT led to tuning of dielectric response in terahertz range. Sr0.9Ca0.1TiO3 exhibited a smeared-out maximum; for x ≥ 0.3, the real and imaginary components of dielectric permittivity (e′) and (e″) decreased with increasing x. These results may offer considerable insights into the application of Sr1−xCaxTiO3 in smart THz device.