Search

In the present contribution special attention is paid to the spectroscopic and thermal characterization of MgI 2 ·8H 2 O which is the stable hydrated form at room temperature. The infrared spectra of MgI 2 ·8H 2 O and its deuterated analogues recorded at room and liquid nitrogen temperature are presented and interpreted. In the low-temperature diference infrared spectrum of the slightly deuterated analogue (≈5% D) at least four bands are found out of the expected five (at 2595, 2550, 2538 and 2495 cm −1 ) as a result of the uncoupled O–D oscillators in the isotopically isolated HOD molecules. Multiple bands are observed in the water bending region and only two bands of the HOH librational modes are found. For more precise and deep description of the processes occurring upon heating of MgI 2 ·8H 2 O we have applied simultaneous TG/DTA/Mass spectrometry technique identifying the gases evolved during the thermal transformations. We have established that the thermal decomposition of MgI 2 ·8H 2 O is a complex process that takes place in two main stages. In the first stage (between 120 and 275 °C) the salt undergoes a partial stepwise dehydration to MgI 2 ·2H 2 O followed by a hydrolytic decomposition with formation of magnesium hydroxyiodide Mg(OH) 1.44 I 0.56 accompanied with simultaneous release of H 2 O and HI. In the second stage Mg(OH) 1.44 I 0.56 is completely decomposed to MgO with elimination of gaseous H 2 O, HI, I 2 and H 2 . Infrared spectra of the annealed samples heated between 190 and 270 °C confirmed the formation of magnesium hydroxyiodide. [ABSTRACT FROM AUTHOR]

In this work, we present first data on the infrared and Raman spectroscopic characteristics, thermal analysis and solid-state transformations of MgKH(AsO)·15HO, which is a unique example of an acid salt containing dimeric units [H(AsO)] in its crystal structure. The infrared and Raman spectra recorded at ambient conditions have been studied, and an assignment of the observed vibrational bands has been proposed considering the crystal structure data. The thermal behavior of MgKH(AsO)·15HO has been investigated by simultaneous TG/DTA/mass spectrometry experiments in the temperature range up to 1000 °C at different heating rates, and new data on the thermal stability and thermal dehydration of MgKH(AsO)·15HO have been obtained. The phase composition after the dehydration processes in the temperature interval of 300-650 °C has been studied by combination of powder XRD and IR spectroscopic analyses. The spectroscopic and thermal properties of MgKH(AsO)·15HO have been compared to those of the isostructural phosphate salt MgKH(PO)·15HO. [ABSTRACT FROM AUTHOR]

We report precursor-based methods for low-temperature synthesis of two structure modifications of NaMnPO4. The maricite phase is thermodynamically more stable, while the olivine phase is of great interest as a positive-electrode material for lithium and sodium ion batteries. The advantage of synthetic procedures is the formation of defectless NaMnPO4 in the temperature range of 200–400 °C. The structure and morphology characterizations of two modifications are performed by powder XRD, SEM and TEM analyses. The oxidation state of the Mn ions in NaMnPO4 is determined by X-ray photoelectron spectroscopy. The local environment of Na in both structure modifications is assessed by 23Na MAS NMR spectroscopy. The synthesis methods are based on the formation of appropriate precursors that are easily transformed to target NaMnPO4. Thermal decomposition of freeze-dried phosphate–formate precursor yields NaMnPO4 with a maricite structure at 400 °C. KMnPO4·H2O with a dittmarite-type structure acts as a structure-template precursor for the preparation of NaMnPO4 with an olivine structure by an ion exchange reaction. Both olivine and maricite NaMnPO4 do not accommodate any anti-site mixing and Na,Mn deficiency. The morphology of NaMnPO4 consists of nano-sized particles (less than 50 nm) that are closely bound together into aggregates, the shape of the aggregates being dependent on the synthesis procedure used. [ABSTRACT FROM AUTHOR]