Crystallisation of VOHPO4·0.5H2O Original Research Article

The crystal growth process for VOHPO4·0.5H2O in organic media has been studied. In situ energy-dispersive X-ray diffraction has identified a phase at short reaction times (<300 s) at a d-spacing of 7.5 Å, which shifted to 6.7 Å during the first 20 min of synthesis and disappeared as VOHPO4·0.5H2O formed. The phases observed at short reaction times is tentatively identified as VOPO4·2H2O and VOPO4·H2O. At short reaction times, these platelets appeared as thin square platelets (10 μm×10 μm) were observed in each sample by microscopy and energy-dispersive X-ray analysis confirmed that they contained phosphorus and vanadium. After synthesis times of about 20 min, these platelets appear to delaminate, sometimes at the edge and sometimes at the centre of the platelets. Evidence is presented that VOHPO4·0.5H2O nucleates and grows from the delaminated edges. Here we present the hypothesis that the folded platelet edges generated in the delamination process, possibly as VOPO4·2H2O converts to VOPO4·H2O and act as the nucleation point from which the VOHPO4·0.5H2O phase grows epitaxially into the familiar rosette like habit. The (0 0 1) and (2 0 1) planes of VOHPO4·0.5H2O are associated with the epitaxial growth.