Low temperature structural phase transition in hafnium and zirconium tetrafluoride trihydrates

From time-differential perturbed angular correlation (TDPAC) measurements, the monoclinic and triclinic crystal structures in hafnium and zirconium tetrafluoride trihydrates are found to be present simultaneously in both the compounds. From previous TDPAC and XRD investigations, a monoclinic crystal structure for HfF4·3H2O but, for its analogues zirconium compound, a triclinic structure was reported. Contrary to earlier reports, the triclinic fraction in HfF4·3H2O is found to be maximum (80%) at room temperature. In fact, the triclinic crystal structure of HfF4·3H2O is reported here which was not known prior to this report. In ZrF4·3H2O, a strong signal (80–90%) for the triclinic structure is found at room temperature while the monoclinic fraction appears as a weak signal (10–15%). Structural phase transitions in these trihydrate compounds have been observed in the temperature range 298–333K. •HfF4·3H2O and ZrF4·3H2O are investigated by TDPAC.•Both monoclinic and triclinic crystal structures are found at 298K.•Triclinic structure of HfF4·3H2O is reported for the first time.•Structural phase transitions in both compounds are found in the range 298–333K.•HfF4·3H2O transforms at 333K and produce four different compounds.