Optical vibrational properties of Bi2-xCaxSn2O7-x/2 ceramics

Abstract

Bi2-xCaxSn2O7-x/2 ceramics were synthesized by solid-state reactions and sintered at 1050 °C. Raman and infrared spectroscopies were used to investigate the optical vibrational properties of pure Bi2Sn2O7 ceramics, as well as to understand the influence of Ca2+ substitution for Bi3+ on the vibrational characteristics of the Bi2-xCaxSn2O7-x/2 system (for x ≤ 0.02). First, we demonstrate that partial substitution of Bi3+ with Ca2+ ions does not promote the β-phase, as it is commonly reported for other cationic substituents. The results of Raman and infrared spectroscopies showed that 34 bands were observed by Raman scattering, and 22 modes were observed by infrared spectroscopy. It was also verified that Raman scattering was quite sensitive to the morphological features of the samples, which was not the case for infrared spectroscopy. Scanning electron microscopy on the sintered samples showed that such sensitivity is partially linked to the grain sizes, which are larger than the incident light beamwidth, but smaller than the infrared beamwidth. Thus, infrared spectroscopy takes contributions from the average of a number of grains, while Raman spectroscopy evaluates contributions of single grains. The dielectric merit factors of the Bi2Sn2O7 ceramics were also obtained from infrared spectroscopy, namely ɛ0 = 24.2 and Qu×f = 56.9 THz. Finally, it is worth noting that this paper presents the first investigation of infrared spectra of Bi2-xCaxSn2O7-x/2 materials.