Influence of the temperature and phase state of K,Ca/NO3 and K,Mg/NO3 binary systems on the vibrational anharmonicity and orientational mobility of the nitrate ion

Abstract

The absorption spectra of homogeneous and heterophase melts and glasses of the K,Ca/NO 3 and K,Mg/NO 3 systems are studied by IR Fourier spectroscopy. The temperature-phase dependences for the first and second order spectra are analyzed, and the anharmonicity constants for internal vibrations of the nitrate ion are estimated. The influence of finely dispersed Al 2 O 3 powder on the structural-dynamic properties of the K,Ca/NO 3 and K,Mg/NO 3 systems is studied. A mechanism for charge transfer in heterophase nitrate glasses is proposed.Introduction. It has been found previously [1,2] for the case of salt glasses in the K,Ca/NO 3 and K,Mg/NO 3 systems that adding a solid filler in the form of a finely dispersed powder (Al 2 O 3 , SiO 2 , CaF 2 ) causes an increase in the electrical conductivity of the filled glass by several orders of magnitude. This means that the heterophase salt glasses are close to the composite solid electrolytes [3,4]. Unlike for the crystals, for salt glasses the effect of a solid filler on their electrical conductivity is universal and shows up in various vitrifying salt systems. The possibilities of using heterophase salt glasses as composite solid electrolytes appear to be important, since this increases the number of possible compositions through varying the form and size of the filler (from nanosizes upward), the composition of the multicomponent salt system, etc. Thus, studies of homogeneous and heterophase salt glasses are of considerable interest, both from the standpoint of clarifying the mechanisms for supercooling and vitrification of a specific class of ionic fluids such as the salt glasses, and in terms of expanding the prospects for their use as glassy ionic conductors. A directed search for the optimum composition of heterophase salt systems which will provide for the highest performance of these as composite solid electrolytes will require studies of their structural and dynamic properties and a detailed clarification of the mechanisms for ion mobility in them. Success along this path will require suitable information on the structural-dynamic properties of the salt system at a molecular level, and on the influence of the temperature, composition, and phase state of the salt system on the character of the local surroundings of a molecular ion and on its spectral characteristics and reorientational mobility. This information can be obtained by the methods of vibrational spectroscopy. Although earlier studies of the Raman scattering spectra of homogeneous and heterophase nitrated glasses have yielded some results [5, 6] on their structural-dynamic properties and the role of solid fillers in raising their ion-conduction properties, much has remained unclear.The goal of this paper is to obtain more complete information on the spectroscopic manifestations of changes in the temperature and phase state of melts and glasses of K,Ca/NO 3 and K,Mg/NO 3 systems, on the structural-dynamic properties of heterophase systems, and on possible mechanisms for ion mobility in them.Experiment. T...