Ionic transport and heat capacity of glass-forming metal-nitrate mixtures

Ionic transport of the glass-forming metal - nitrate mixtures [Ca(NO₃)₂]_0.4[RbNO₃]_0.6 (CRN), [Mg(NO₃)₂]_0.44[KNO₃]_0.56 (MKN), and [Mg(NO₃)₂]_0.44[NaNO₃]_0.56 (MNN) was investigated near the glass transition using broadband spectroscopy of the complex conductivity to 300 MHz. The real part of the conductivity exhibits a transition from frequency independent to power law behavior as found in most ionic conductors. At high frequencies the frequency exponent approaches unity and becomes larger at low temperatures. In the real part of the dielectric constant, a relaxation step could be observed in CRN. A detailed evaluation of the results within the modulus formalism is presented. The imaginary part of the electrical modulus exhibits well developed peaks which are described by the Kohlrausch-Williams-Watts function. All materials studied can be characterized as fragile glass formers. The results are compared to findings in [Ca(NO₃)₂]_0.4[KNO₃]_0.6 (CKN). Low temperature heat capacity, for three nitrate glass-formers, including CKN, exhibits weak excess contributions near 10 K.