Correlation between the chromaticity, dielectric properties and structure of the binary metal pyrophosphates, Cu(2−x)ZnxP2O7

Abstract

The binary metal pyrophosphates, Cu_(2−x)Zn_xP₂O₇; x = 0.50–1.50, were synthesized via solid state reaction in order to obtain information on their solid solution phase formation. Characteristic peaks of the β-phase were detected under UV/Vis light emission in the range of 1200–1250 cm⁻¹. The P₂O₇⁴⁻ ion, analyzed through vibration, carried the O–P–O radical, P–O–P bridge, and approximate M–O bond stretching, and was identified using Raman and Fourier transform infrared (FT-IR) spectra. The corrected dielectric constant (ε_r) of the samples showed a similar value when Cu²⁺ was replaced by Zn²⁺ in the Cu₂P₂O₇ structure. However, a slightly decreasing ε_r could still be seen when the component x increased. The color of the samples with x = 0.00–1.50 exhibit a greenish hue, except for the composition with x = 2.00, which presents a colourless powder. The CIE chromaticity coordinates of Cu_(2−x)Zn_xP₂O₇; x = 0.50 to 1.50, shifted from (0.303, 0.366) to (0.292, 0.388), thus corresponding to a visible wavelength that shifted from about 506 to 512 nm, and 561 nm for x = 0.00. The phenomena of both dielectric and optical properties resulted from the changing crystal structure of the respective P₂O₇⁴⁻ cluster and octahedral M–O₆ site. Investigation of the crystal structure was carried out by using Rietveld refinement analysis, with support from the extended X-ray absorption fine structure (EXAFS) fitting technique. Furthermore, this study revealed the relationships for binary metal pyrophosphates between their structure and dielectric properties, and the correlation between their structure and optical properties, which was confirmed by the reduction in chemical bonding, bond angle, number of clusters, and distortion of the octahedral MO₆.