New Green Dielectrics Related to Calcium Titanate: Synthesis and Characterizations

The main purpose of the present work is the preparation of green dielectrics by solid-state reaction between two perovskites: CaTiO3 (CTO) and KMgF3 (KMF). Calcium titanate and potassium magnesium fluoride powders were previously synthesized, respectively, at 850 °C and 700 °C. Several chemical compositions (1–x) CTO + x KMF were then prepared and dry-milled. The mixtures were pressed into pellets and sintered in free air at 950 °C for 2 h. The obtained ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA, DTGA) and dielectric measurements (DE). The XRD study revealed the formation of a fluorinated perovskite solid solution with general formula Ca1–x K x (Ti1–x Mg x )O3–3x F3x (CKTMOF) in the initial composition range 0 ≤ x ≤ 0.20. The diffraction peaks of CKTMOF oxyfluorides were indexed in an orthorhombic lattice, and no significant change was observed in the unit cell parameters with increasing KMF amount. On the other hand, the addition of KMF to CTO allowed the ceramic’s densification at low temperature. The shrinkage increased from 1.9 % (x = 0) to 9.5 % (x = 0.20), and the grain’s size of the various ceramics was in the range 0.5–5μm. Several thermal phenomena were detected by DSC and DE. No weight loss and no peak were depicted on the TGA and the DTGA curves over all the temperature range investigated; therefore, the phenomena observed by DSC and DE could be ascribed to phase transitions. These dielectrics could be of interest for the fabrication of class I capacitors; however, the losses have to be improved.