Correlation Between Structure, Chromaticity, and Dielectric Properties of Calcium Copper Pyrophosphates, Ca2−xCuxP2O7

Abstract

Discoveries of the correlation between the physical properties and structure of the materials are interesting in the field of the material science and chemical engineering. This work investigated the correlation between the structure, chromaticity, and dielectric properties of calcium copper pyrophosphates, Ca2−xCuxP2O7. The solid state thermal decomposition reaction was employed to synthesize the Ca2−xCuxP2O7 by varying the mole ratio between Ca and Cu. The structure and crystallography of the pyrophosphate compounds were identified and confirmed by using an X-ray diffraction (XRD) technique. The Rietveld refinement method and the extended X-ray absorption fine structure (EXAFS) least-squares fitting technique were also applied to refine the sample crystal structure. The bond angle and bond length of samples were also obtained from the refinement method. The X-ray absorption edge energies (E0) of the synthesized compounds were investigated and the obtained results confirmed the formation of the binary metal pyrophosphates (Ca2−xCuxP2O7). The image sensor result of the Cu2P2O7 sample (x = 2.00) illustrated a yellowish-green color, while other compounds (x = 0.50−1.50) presented color tones that changed from blue-green to bluish-green. The dielectric constant (εr) of the synthesized Ca2−xCuxP2O7 were calculated by using the Clausius-Mossotti relation, and the highest εr was observed for Ca2P2O7. The Raman and Fourier transform infrared (FTIR) spectrophotometers were employed to characterize and confirm the vibrational characteristics of the P2O74− group. The experimental results demonstrated that the changing in the crystal structure of Ca2−xCuxP2O7 (i.e., bond angle of P−O−P in P2O74− and distortion phenomena in M−O6 octahedral site) can cause the correlation between the dielectric and optical properties of the sample.