Abstract
We report on the evolution of the mechanical and electrical properties of sodium metaphosphate glasses with addition of sodium sulfate or sodium chloride. The addition of these two sodium salts converts the medium-range order of our glasses from 2D phosphate chains to a mixed 1D + 2D network similar to ionic glasses, while the short-range order of the phosphate units remains unaffected. Replacing the phosphate units by chloride ion monotonically decreases the glass transition temperature, but enhances the Young’s modulus and moderately increases the ionic conductivity. On the other hand, the sulfate group decreases the glass transition temperature as well, though the Young’s modulus remains constant, while the ionic conductivity strongly increases. The changes in conductivity are related to the enhancement of the ionic mobility in these glasses, which in turn affect the size and distribution of the plastic events taking place during indentation-driven deformation.
Highlights
Unlike silicate and borosilicate glasses, phosphate glasses are mainly explored for specialty applications, such as laser gain media, hermetic seals, nuclear waste immobilization, and biomaterials (Brow, 2000)
These glasses allow for a comparison between the behavior of Na+ cations when only coordinated by non-bridging oxygens or when in a mixed halide and oxyanion environment, providing an interesting control group to whether the mechanical and electrical properties are more sensitive to changes in the overall packing density or to the chemistry of the anions coordinating the cationic modifier
In the Raman spectra of the NaPO3-Na2SO4 glasses in Figure 1, the appearance of a peak at ∼1,000 cm−1 is assigned to the symmetric stretching νs(SO24−) (Da et al, 2011; Thieme et al, 2015) and it increases in intensity with increasing Na2SO4 concentration
Summary
Unlike silicate and borosilicate glasses, phosphate glasses are mainly explored for specialty applications, such as laser gain media, hermetic seals, nuclear waste immobilization, and biomaterials (Brow, 2000) Another potential application is their use as solid electrolytes for ion-conducting solid state batteries (Jun et al, 1990; Kim et al, 2015) due to their high ionic conductivity at room temperature ranging from 10−5 to 10−3 S.cm−1 (Martin and Angell, 1986). These glasses allow for a comparison between the behavior of Na+ cations when only coordinated by non-bridging oxygens or when in a mixed halide and oxyanion environment, providing an interesting control group to whether the mechanical and electrical properties are more sensitive to changes in the overall packing density (where both the Cl− and SO24− should behave when taking their respective sizes into account) or to the chemistry of the anions coordinating the cationic modifier (where the NaPO3 and the sulfate bearing glasses should be comparable, while the sodium chloride glasses should behave differently)
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