Low temperature phase transition and crystal structure of CsMgPO{sub 4}

Journal Article · Thu Jan 15 04:00:00 EST 2015 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2014.09.037· OSTI ID:22443501

Orlova, Maria ^[1]; Khainakov, Sergey ^[2]; Michailov, Dmitriy ^[3]; Perfler, Lukas ^[1]; Langes, Christoph ^[4]; Kahlenberg, Volker ^[1]; Orlova, Albina ^[3]

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1. Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria)
2. Departamento de Química Física y Analítica, Universidad de Oviedo—CINN, 33006 Oviedo (Spain)
3. Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation)
4. Institute of Pharmacy, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria)

CsMgPO{sub 4} doped with radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at temperatures close to ambient conditions (∼−40 °C) was observed. Information about such kind of structural changes is important in order to understand whether it can cause any problem for medical use of this compound. The phase transition has been investigated in detail using synchrotron powder diffraction, Raman spectroscopy and DFT calculations. The structure undergoes a transformation from an orthorhombic modification, space group Pnma (RT phase) to a monoclinic polymorph, space group P2{sub 1}/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2) Å, b=8.95501(1) Å, c=5.50344(2) Å, β=90.68583(1)°, V=472.198(3) Å{sup 3}. CsMgPO{sub 4} belongs to the group of framework compounds and is made up of strictly alternating MgO{sub 4}- and PO{sub 4}-tetrahedra sharing vertices. The cesium counter cations are located in the resulting channel-like cavities. Upon the transformation a combined tilting of the tetrahedra is observed. A comparison with other phase transitions in ABW-type framework compounds is given. - Graphical abstract: Structural behavior of β-tridymite-type phosphate CsMgPO{sub 4}, considered as potential chemical form for radioactive Cs-source has been studied at near ambient temperatures. A phase transition at (∼−40 °C) has been found and investigated. It has been established that the known orthorhombic RT modification, space group Pnma, adopts a monoclinic cell with space group P2{sub 1}/n at low temperatures. In this paper, we present results of structural analysis of changes accompanying this phase transition and discuss its possible impact on the application properties. - Highlights: • β-Tridymite type phosphate CsMgPO{sub 4} undergoes so called translationengleiche phase transition of index 2 at −40 °C. • The structure transforms from an orthorhombic (space group Pnma) to a monoclinic (space group P2{sub 1}/n) phase. • In comparison with the RT form, the LT modification adopts a similar but slightly distorted unit cell.

• OSTI ID: 22443501
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Vol. 221; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AMBIENT TEMPERATURE
CATIONS
CESIUM
DIFFRACTION
DOPED MATERIALS
MAGNESIUM OXIDES
MONOCLINIC LATTICES
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
PHOSPHATES
POWDERS
RAMAN SPECTROSCOPY
SPACE GROUPS