Peculiarities of phase transitions and physical properties in (NH₄)₂SbF₅

Abstract

BY1,. M. AVKHUTSKII (a), R. L. DAVIDOVICH (a), L. A. ZEMNUKHOVA (a), P. S. GORDIENEO (a), V. URBONAVI~IUS (b), and J. GRIGAS (b) The dynamics of the (NH,),SbF, crystal lattice showing the superionic phase transition is studied in a broad temperature interval by NMR and NQR methods, together with electrophysical and calorimetrical properties. The investigations establish the ionic state of the axial fluorine atom in relation to equatorial atoms in the [SbF,I2-complex. The successive phase transitions are revealed and the mechanism of phase transitions is elucidated. The phase transitions are caused by the reorientation movements of NH, and [SbF,IZ-groups. The paper also describes the influence of water solution inclusions in the crystal on the superionic phase transition.Es wird die Dynamik des Kristallgitters mit den Methoden der NMR, NQR, sowie auch die elektrophysikalischen und kalorimetrischen Eigenschaften von (NH,),SbF,-Kristallen, in denen ein superionischer Phasenubergang gefunden wird, in einem breiten Temperaturintervall nntersucht. Die Ionenbindung des axialen F-Atoms ist vie1 starker als die Ionenbindung der aquatorialen P-Atome der [SbF,]2--Gruppe. Es wird eine Phasenubergangsfolge in diesen Kristallen gefunden und ein Mechanismus dieser Phasenubergange vorgeschlagen. Die Phasenubergange werden durch Drehung von NH,-und [SbF,I2--Gruppen vernrsacht. Es wird auch der EinfluB der im Kristall befindlichen Wasserlosnngsinklusionen auf den superionischen Phasenubergang diskutiert.

Nuclear Magnetic and Quadrupole Resonance Studies of Phase Transitions in Crystalline (NH4)2SbF5 and (ND4)2SbF5

“…However, when the drying was incom plete, there appeared another relatively large peak around 248 K and a small anomaly centering at 165 K, which is superposed on the lower transition. These facts suggest strongly that the anomalies de tected in the previous measurements of the heat ca pacity and the electric conductivity in [4] and [5] were caused by trace of occluded water in the sample.…”

“…We now attempted to track down the source of the discrepancy between our previous results and those reported in [4] and [5] by changing the conditions of the sample preparation. We also made more detailed measurements of the NQR frequencies for the anti mony isotopes as well as of the spin-lattice relaxation times for proton and fluorine in order to clarify the nature of the phase transitions in this substance.…”

“…The lower transition was identified as an order-disorder transi tion with respect to the orientation of the ammonium ions, and the upper one was inferred to be a kind of displacive structural transition associated with some angular displacement of the square-pyramidal SbF5 2 -anions. Urbanovitschyus et al measured the complex dielectric constant and the electric conductivity on this material and found a phase transition at 257 K, above which, they reported, the crystal became highly conductive [4], Later, Avkhutskii et al measured the wide-line nuclear magnetic resonance, the antimony nuclear quadrupole resonance (NQR), and the heat capacity and reported that at least three phase transi tions occur at 169, 257, and 290 K [5],…”

Optical Investigations of Phase Transitions in (NH4)2SbF5Crystal

“…Successive phase transitions were reported in (NH4)2SbF5 crystal [1][2][3][4][5][6][7][8]. However, there are discrepancies related to the number of the phase transitions in this compound.…”

“…In the temperature range 138-294 K monoclinic symmetry (space group C2/c) is proposed. In the papers [1][2][3] a transition to superionic phase at 257 K is implied. however, nuclear quadrupole resonance (NQR) measurements [5] gave evidences for two phase transitions at 292 K and 169 K only.…”