• journal_title：European Journal of Mineralogy
• Contributor：Elena Yu Borovikova ; Victoria Kurazhkovskaya ; Dmitriy Ksenofontov ; Yuriy Kabalov ; Vladimir Pet’kov ; Elena Asabina
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2012/0024-2209
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：24
• issue：5
• firstpage：777
• section：Articles

Caesium-bearing phosphates with the β-tridymite structure are considered as storage container for radioactive Cs. In this context, double phosphates of caesium and divalent cations, CsM²⁺PO₄ where M²⁺ = Zn, Co, Mn, Mg, and Ni, have been synthesised by the precipitation method as powders and investigated by infrared spectroscopy in combination with factor-group analyses for band assignment. Comparison of the IR pattern of CsZnPO₄ and CsCoPO₄ confirms that they are isomorphic (space group P1 2₁/a 1 at room conditions). Both undergo T-induced phase transitions: one at 260 °C (Pn2₁a) and another one at 310 °C (Pnma). High-temperature IR spectra of the orthorhombic modifications of CsZnPO₄ are presented and assigned. Comparison of the IR-spectrum of CsMnPO₄ with that of CsZnPO₄ (Pn2₁a) confirms that it crystallizes in the orthorhombic structure at room conditions (Pn2₁a). CsMgPO₄ crystallizes at room conditions in the orthorhombic space group Pnma, however, it tends to hydrate immediately after quenching in air forming the cubic hydrate CsMgPO₄·6H₂O (space group F4̄3m). The liability to hydration is also characteristic for CsNiPO₄. Temperature-dependent IR spectroscopy, X-ray diffraction, thermal analyses (TGA, DTA) and second-harmonic generation (SHG) revealed that pure anhydrous CsMgPO₄ (space group Pnma) can only be stored in air at temperatures higher than 150 °C. Our study proves that CsM²⁺PO₄, where M²⁺ = Zn, Co, Mn, may be stable containers for radioactive Cs at room temperatures. However, CsMgPO₄ and CsNiPO₄ can only be used as crystalline matrices for the immobilisation of radioactive Cs when stored at temperature higher than 150 °C due to their hydrolytic instability in air. The difference in the structures of CsMg phosphate and Cs phosphates with Zn, Co, and Mn is caused by the different liability of these cations to form either ionic or covalent chemical bonds.