Abstract
Emerald green crystals of the new composition CuHPO4were synthesized and compared to (copper metaphosphate) Cu2P4O12and (copper ultraphosphate) Cu2P8O22. Various copper ultraphosphate and metaphosphate glasses of different compositions between pure P2O5and Cu2P4O12were melted in crucibles or in evacuated and sealed silica ampoules at 1473 K or 1373 K for 2 hrs. The UV-VIS-spectra and the IR-spectra of all crystals and glasses were measured and compared. The absorption band of Cu2+was resolved into more component Gaussian bands and differentiated between square-pyramidal and octahedrally coordinated copper. These structural changes are responsible for colour changes from green to turquoise. The infrared spectroscopic properties of the copper phosphate glasses differ between metaphosphate and ultraphosphate structures but show similarities between the crystals and the glasses of the same structure type. EPR studies of some of the glasses show different kinds of spectra, with increasing copper content.
Highlights
Orthophosphoric acid condenses to diphosphoric acid under heat treatment
The infrared spectroscopic properties of the copper phosphate glasses differ between metaphosphate and ultraphosphate structures but show similarities between the crystals and the glasses of the same structure type
After one week tempering at 373 K, emerald-green needles of the composition CuHPO4 grow, if phosphoric acid (65%) is used
Summary
Orthophosphoric acid condenses to diphosphoric acid under heat treatment. The related salts are called diphosphates (pyrophosphates), which contain P2O7 groups, for example, copper hydroxydiphosphate Cu3[P2O6OH]2 [1] and copper pyrophosphate α-Cu2P2O7 [2]. Ultraphosphates show linked together Q2 and Q3 (2- and 3-cornerlinked PO4 tetrahedra) and build layer or chain structures. It is differentiated between nonbonded (Q0) monophosphates, primary bonded (Q1) diphosphates, secondary bonded (Q2) meta- and cyclophosphates, and tertiary bonded (Q3) framework phosphates (pure P2O5). The glasses exhibit changes in structure and properties, like density and colour [15,16,17]. These changes are important for possible applications and need further investigations. The metaphosphate glasses studied with UV-VIS-spectroscopy were melted in a crucible and cooled under different conditions
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