title: High-Pressure Phase Transformations in TiPO4: A Route to Pentacoordinated Phosphorus.
abstract: Titanium(III) phosphate, TiPO4, is a typical example of an oxyphosphorus compound containing covalent P-O bonds. Single-crystal X-ray diffraction studies of TiPO4reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high-pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO4-V is the first inorganic phosphorus-containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO4-V coexists with TiPO4-IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO4-II is found to be an incommensurately modulated phase whereas a lock-in transition at about 7 GPa leads to TiPO4-III with a fourfold superstructure compared to the structure of TiPO4-I at ambient conditions. TiPO4-II and TiPO4-III are similar to the corresponding low-temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin-Peierls interactions.
authors: Bayerisches Geoinstitut, University of Bayreuth, 95440, Bayreuth, Germany.|Laboratory of Crystallography, University of Bayreuth, 95440, Bayreuth, Germany.|Materials Modeling and Development Laboratory, National University of Science and Technology "MISIS", 119049, Moscow, Russia.
authors: Maxim
authors: 0000-0003-0248-1728
authors: M
authors: Bykov
authors: Bayerisches Geoinstitut, University of Bayreuth, 95440, Bayreuth, Germany.
authors: Elena
authors: E
authors: Bykova
authors: ESRF, 38000, Grenoble, France.
authors: Michael
authors: M
authors: Hanfland
authors: Deutsches Elektronen-Synchrotron (DESY), 22607, Hamburg, Germany.
authors: Hanns-Peter
authors: HP
authors: Liermann
authors: Max Planck Institute for Solid State Research, 70569, Stuttgart, Germany.
authors: Reinhard K
authors: RK
authors: Kremer
authors: Institute of Inorganic Chemistry, University of Bonn, 53121, Bonn, Germany.
authors: Robert
authors: R
authors: Glaum
authors: Bayerisches Geoinstitut, University of Bayreuth, 95440, Bayreuth, Germany.
authors: Leonid
authors: L
authors: Dubrovinsky
authors: Laboratory of Crystallography, University of Bayreuth, 95440, Bayreuth, Germany.
authors: Sander
authors: 0000-0001-9645-8240
authors: S
authors: van Smaalen
keywords: X-ray diffraction; high-pressure chemistry; phase transitions; phosphorus; spin-Peierls compounds