title: High-temperature crystal structures and chemical modifications in RbH(2)PO(4).
abstract: We have used laboratory and synchrotron x-ray diffraction to investigate the structural and chemical changes undergone by polycrystalline RbH(2)PO(4) upon heating within the 30-250 °C temperature interval. Our data show no evidence of the previously reported onset of partial polymerization at T = 96 °C (Park et al 2001 J. Phys.: Condens. Matter 13 9411) which was proposed as an explanation for the high-temperature proton conductivity enhancement in phosphate-based solid acids. Instead, we found that a tetragonal [Formula: see text] monoclinic polymorphic transition initiates at T≈90 °C. The transition is complete at T≈130 °C, and the new monoclinic RbH(2)PO(4) polymorph is stable upon further heating to T = 200 °C. Moreover, its crystal structure is isomorphic to that of monoclinic CsH(2)PO(4). This remarkable similarity suggests that the microscopic structures and dynamics responsible for the high-temperature superprotonic behavior of RbH(2)PO(4) could be the same as those of its Cs-based counterpart.
authors.affiliation: Department of Physics, University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968, USA.
authors.forename: Cristian E
authors.initials: CE
authors.lastname: Botez
authors.forename: Heber
authors.initials: H
authors.lastname: Martinez
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Tackett
authors.forename: Russell R
authors.initials: RR
authors.lastname: Chianelli
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Zhang
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Zhao