Crystal Structure of γ‐Ca₂P₂O₇

Abstract

Three polymorphs of calcium pyrophosphate, Ca2P2O7, are known. Here the crystal structure of γ‐Ca2P2O7 is described for the first time. The crystal structure could be solved from powder X‐ray data. The results were confirmed by 31P high‐resolution solid‐state NMR spectroscopy measurements and by quantum chemical calculations under period boundary conditions. With the help of spin‐echo experiments the 2J(31P,31P) coupling for the P−O−P bonds could be determined. The different polymorphs can unambiguously be identified from 31P magic‐angle‐spinning NMR spectroscopy. The 31P NMR chemical shift parameters of α‐, β‐ and γ‐Ca2P2O7 were determined from magic‐angle‐spinning experiments at slow spinning frequencies, while a peak assignment was achieved on the basis of gipaw‐calculations and confirmed by the observed J‐coupling values. The polymorph γ‐Ca2P2O7 belongs to the structure type of Cd2P2O7 in the space group Ptrue1‾ ${P\bar 1}$ (a=6.6660 (2) Å, b=6.7220 (2) Å, c=6.7374 (2) Å, α=65.113 (2)°, β=87.763 (2)°, γ=85.076 (2)°).

Influence of Current Duty Cycle and Voltage of Micro-Arc Oxidation on the Microstructure and Composition of Calcium Phosphate Coating

“…It can also be observed that the Ca/P ratio increases with increasing voltage, except in modes A and B 600 V. This may be due to the increased deposition of Ca 2+ ions from the electrolyte [52]. A relatively high Ca/P ratio of 0.62 was observed in the CaP layer produced under mode C at 600 V. This elevated ratio is attributed to the presence of the calcium phosphate phase γ-Ca 2 P 2 O 7 , which has a Ca/P ratio of one [53]. An increase in the Ca/P ratio is beneficial for the formation of calcium phosphate and enhances the bioactivity of the coatings.…”

“…However, increasing the voltage to 600 V causes the temperature in the discharge channels to rise, which can lead to the formation of the CaP crystalline phase γ-Ca 2 P 2 O 7 (PDF 00-017-0499). The Ca 2 P 2 O 7 phase is also biocompatible for use in the production of CaP ceramics for the treatment of bone defects [53,60,61]. Phase formation does not change significantly with current duty cycles; however, in mode C, CaP compounds were formed without titanium phosphates, and crystalline phases were formed at all processing voltages.…”