Unravelling the effects of polaron conduction on mixed conductivity glasses.

FRECHERO M. A.

Polarons : recent progress and perspectives.

Nova Science Publishers

Año: 2018; p. 100 - 122

Oxide glasses are the oldest ever-known glasses. Probably, silicate glasses are the most ancient material of industrial interest. However, glasses formed by other kind of oxides are of uppermost importance because of the special properties which they are able to develop for many applications in electronics, optics, biology, etc. Every oxide that originates a three-dimensional network built by corner connected oxygen polyhedral, with a particular coordination number, conforms a glassy matrix of singular properties. Such properties can be modified by the incorporation of other oxides. In general, each oxide has a specific function, i.e. it could behave as a glass former, a former and a modifier or just a modifier. A huge number of glass compositions can be prepared by different methods which also have an influence on the glass properties. As we are particularly interested in the electrical properties of glasses, in the present chapter, we analyze polaron conductivity in the presence of large ion concentrations, i.e. when the ionic conductivity is not negligible. We analyze the electrical response of uncommon oxide glasses like TeO2, P2O5, B2O3 and Bi2O3 in which several transition metal oxides like V2O5, Cu2O, Ag2O, Nb2O5 and MoO3 have been incorporated in a single or mixed way when some modifier oxides are also present (Li2O, Na2O, BaO, MgO, SrO); the most important difference among them being that they are univalent or divalent cations.Towards the end of the second part of the last century, materials with low charge carrier mobility (<0.1 cm/V.s) appeared posing a challenging problem because the classical transport theory was not able to explain such behavior. In 1959, Holstein proposed that an electron could be trapped and be not capable to move unless the lattices in where it is moved along with it; thus, introducing the polaron concept. That charge carrier (the electron, for example) induces a dipole moment on its surrounding and as a consequence, a new entity, the polaron, is born. Then, polaron conductivity results from the displacement of polarons in a material. During its transport, the polaron has to displace through the material. If the material is a glass, it has to displace through the glassy matrix, i.e. the charge carrier and the distortion in its surrounding. Therefore, we also analyze here, how the presence of large number of mobile cations affects the polaron transportation originated by the existence of transition metal oxides incorporated in non conventional oxide glasses.