Abstract
CsMgPO
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
P
2
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
3
. CsMgPO
4
belongs to the group of framework compounds and is made up of strictly alternating MgO
4
- and PO
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
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
P
2
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
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
P
2
1
/
n
) phase.
• In comparison with the RT form, the LT modification adopts a similar but slightly distorted unit cell.
Page:
224-224
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