Effect of mixed glass network formers on the electrical transport in alkali germano(boro)phosphate glasses

Abstract

Učinak miješanih staklotvoraca istraživan je u četiri serije Li2O/Na2O–(B2O3)–P2O5–GeO2 stakala. Sustavnom zamjenom jednog staklotvorca, P2O5, drugim, GeO2 pri čemu udio alkalijskog iona ostaje nepromijenjen, dolazi do promjena u strukturi staklene mreže koje rezultiraju povećanjem električne provodnosti u svim istraživanim serijama stakala. U ternarnim je serijama lokalizirana difuzija pokretljivih Li+ i Na+ iona olakšana kontinuiranim promjenama u fosfatnoj mreži i nastajanjem miješanih germanofosfatnih strukturnih jedinica. S druge strane, u kvaternim serijama, prisutnost B2O3, uzrokuje bržu depolimerizaciju fosfatne mreže i umrežavanje s B4 jedinicama zbog čega su pri niskim udjelima GeO2 vrijednosti DC provodnosti više od odgovarajućih stakala iz ternarne serija. Međutim, pri višim udjelima GeO2 nastaju dodatne miješane jedinice koje utječu na umreženost staklene mreže. Nehomogenosti u staklenoj mreži stvaraju više zamki za Li+ i Na+ ione zbog čega je porast DC provodnosti slabije izražen. Također, litijeve serije pokazuju više vrijednosti DC provodnosti u odnosu na odgovarajuća stakla iz natrijevih serija jer manji ion Li+ može lakše i brže difundirati kroz staklenu mrežu.The mixed glass network former effect was investigated in four series of Li2O/Na2O–(B2O3)– P2O5–GeO2 glasses. Systematic replacement of one glass network former, P2O5, by another, GeO2, while keeping the alkali ion content constant, causes structural modifications of the glass network, resulting in electrical conductivity enhancement for all four glass series. In ternary series, localized diffusion of mobile Li+ and Na+ ions is facilitated by continuous changes in the phosphate network structure and the formation of mixed germanophosphate structural units. On the other hand, in quaternary series, the presence of B2O3 causes depolymerization of the phosphate network and cross-linkages with B4 units, which makes the DC conductivity values higher than those for the corresponding glasses from ternary series at low germanate content. However, at higher GeO2 content, additional mixed units are formed that affect the connectivity of the glass network. The inhomogeneities in the glass network create more traps for Li+ and Na+ ions, which makes the increase in DC conductivity less pronounced. Also, the lithium glasses show higher values of DC conductivity than the corresponding sodium glasses because the smaller Li+ ion can diffuse more easily and faster through the glass network