Structures of two new high-pressure forms of AlPO₄by X-ray powder diffraction and NMR spectroscopy

Abstract

The crystal structures of two new high-pressure AlPO(4) phases are reported. One phase synthesized at 6 GPa and 1523 K is triclinic (P1) whilst the other phase synthesized at 7 GPa and 1773 K is monoclinic (P2(1)/c). (31)P MAS (magic-angle spinning) NMR suggests three tetrahedral P sites with equal abundance in both phases. (27)Al 3Q MAS NMR spectra provided evidence for two octahedral sites and one five-coordinated Al site in each phase. The crystal structures were solved using an ab initio structure determination technique from synchrotron powder X-ray diffraction data utilizing the local structural information from NMR, and were further refined by the Rietveld method. Both phases contain doubly bent chains made of six edge-shared Al polyhedra (including five-coordinated Al), which are joined by PO(4) tetrahedra. The P1 phase is isostructural with FeVO(4) and AlVO(4). The two phases differ in the packing manner of the chains. This study has demonstrated that the combined application of ab initio structure determination via X-ray powder diffraction and solid-state NMR spectroscopy is a powerful approach to the rapid solution of complex inorganic crystal structures.

Crystal structures of Zn2SiO4 III and IV synthesized at 6.5–8 GPa and 1,273 K

“…Note that the pressure conditions for the syntheses of phases III (6.5 GPa) and IV (7-8 GPa) in this study are somewhat (*2 GPa) lower than those reported in Syono et al (1971). This could be due to difference in pressure calibration: the pressure calibration of Syono et al (1971) was done at room temperature and that used in the present study was performed under high pressure and high temperature conditions using synchrotron radiation (Kanzaki et al 2011).…”

“…The temperature was measured with a W 97 Re 3 -W 75 Re 25 thermocouple with uncertainties within ca 2 K. For samples #2 and #5, the temperature was estimated from the heating power with uncertainties within ca 100 K because the thermocouple failed. The pressure was estimated from a pressure calibration curve constructed from an in situ X-ray diffraction study with the same pressure cell (Kanzaki et al 2011) with an uncertainty of less than 0.5 GPa.…”

Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi₃O₈^.H₂O) and its anhydrous form (kokchetavite)

“…K -cymrite was then synthesized at 5 GPa and 800 °C for 2 hrs using a Kawai -type multi -anvil press. The procedure for the high -pressure and high -temperature experiments is identical to that reported in Kanzaki et al (2011). The anhydrous form (kokchetavite) was produced at ambient pressure by heating K -cymrite at 550 °C for 1hr.…”

Calibration of berlinite (AlPO4) as Raman spectroscopic pressure sensor for diamond‐anvil cell experiments at elevated temperatures

“…In addition, berlinite may well be applicable as pressure sensor at higher pressures than quartz, because the high‐pressure analogues of coesite, stishovite, and post‐stishovite in the system AlPO 4 have not yet been reported . However, three new triclinic or monoclinic AlPO 4 high‐pressure phases have recently been synthesized between 5 to 7 GPa and 1000°C to 1500°C . In a few systems, berlinite forms solid solutions by substitution of Al with B, Ga, or Fe and of PO 4 by AsO 4 , with substantial effects on the frequency of some Raman modes .…”