Département de Physique, Institut préparatoire aux études d'ingénieurs de Sfax, Route Menzel Chaker km 0.5, BP 805, 3018 Sfax, Tunisia
Département de Physique, Institut préparatoire aux études d'ingénieurs de Nabeul, Tunisia
Laboratoire de l'état solide, Faculté des Sciences de Sfax, 3038 Sfax, Tunisia
A new mixed acid sulphate K0.9Rb0.1HSO4 was synthesized at room temperature. It has been firstly characterised by X-ray diffraction (XRD) and vibrational spectroscopy investigations. Then, in order to detect phase transitions and watch changes in the conductivity behaviour, investigations by differential scanning calorimetry (DSC), (XRD), electrical conductivity measurements, and impedance spectroscopy were carried out. The XRD results on single crystals showed that at room temperature, K0.9Rb0.1HSO4 has an orthorhombic symmetry with space group Pbca. The unit cell parameters are: a = 8.39(6) Å; b = 9.79(8) Å and c = 18.98(5) Å. The Raman and infrared spectra at room temperature were also investigated. The structural similarity with KHSO has been confirmed. The thermal studies showed that K0.9Rb0.1HSO4 undergoes two structural phase transitions at about 400 K and 435 K. A partial substitution of K+ by Rb+ increases the conductivity even at room temperature. The transition at 435 K leads to a super-ionic conductor state at high temperatures related with rotational motions of HSO4 − ions.
(Received September 25 2001)
(Revised January 31 2002)
(Accepted February 21 2002)
(Online publication May 15 2002)