The thermal behaviour of the quadrupole hyperfine interaction in (NH4)2HfF6
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A TDPAC investigation has been accomplished on (NH4)2 HfF6 between 14 and 620 K. A phase transition was observed below 390 K. The low temperature phase is characterized by two non-equivalent sites for hafnium atoms in a 1∶1 ratio. The high temperature phase, on the other hand, is depicted by a unique quadrupole interaction. Above 400 K, the compound decomposes successively to NH4 HfF5, NH4 Hf2F9 and HfF4. An enthalpy of 76±4 kJ/mol could be determined for the (NH4)2 HfF6→NH4 HfF5+NH4F chemical reaction. The hyperfine interaction and thermal evolution of (NH4)2 HfF6 was found to be quite similar to that of (NH4)2 ZrF6.
KeywordsThin Film Enthalpy Phase Transition Thermal Behaviour Hafnium
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