Monoclinic RbD2PO4: Room temperature synthesis, chemical and structural stability upon heating

Abstract Monoclinic RbD 2 PO 4 polycrystals (DRDP) were synthesized via the room temperature crystallization of RbH 2 PO 4 (RDP) dissolved in D 2 O. Powder X-ray diffraction (XRD) data collected at T  = 25 °C indicate that this deuterated compound crystallizes in spacegroup P2 1 /m with unit cell parameters a  = 7.688 A, b  = 6.192 A, c  = 4.781 A and β  = 109.02°, and is isomorphic with the intermediate-temperature phase of its hydrogenated counterpart RDP. We found no evidence of a previously reported [ Phase Transitions 80 , 17 (2007)] polymorphic phase transition in DRDP upon heating from room temperature to 210 °C. All lattice parameters vary smoothly within this temperature range, demonstrating that the P2 1 /m phase persists upon heating. In addition, the unit cell volume of monoclinic DRDP is ∼1% greater than that of its RDP polymorph at all temperatures between 150 °C and 210 °C, which indicates the absence of significant deuterium-hydrogen isotope exchange. Further heating to 240 °C leads to the thermal decomposition of the title compound via dehydration.