Achieving high electrical homogeneity in (Na2O, K2O)–Nb2O5–SiO2-MO (M = Ca2+, Sr2+, Ba2+) glass-ceramics for energy storage by composition design

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The Na2O–K2O–Nb2O5–SiO2 glass matrixes modified by alkaline-earth metals oxide MO (M = Ca2+, Sr2+ and Ba2+) with different field strength (Fs) are prepared. The degree of polymerization (DOP) of the glass network structure is enhanced with the addition of MO. The (35-x)Na2O–5K2O–40Nb2O5–20SiO2-xMO glass are crystalized at the exothermic peak 916 °C as evidenced by an exothermic peak in thermal analysis. The crystallization kinetics are analyzed by crystallization activation energy (Ec) which increases with the addition of MO facilitating the homogenous nucleation. The crystallinity and the fraction of crystalline phase of the glass-ceramics are analyzed by structural refinements. The dielectric permittivity and polarization of the glass-ceramics are researched. The electrical homogeneity of glass-ceramics is discussed on different scales. On the grain scale of the glass-ceramics, the uniform microstructure prevents the free charge from accumulating. On the glass network scale, the tight glass network structure prevents large interface polarization caused by the accumulating of space charge. A large binding energy (W) or minimum hopping distance (Rm) prevents the electrons from hopping. Kelvin probe force microscopy (KPFM) is used to test the potential of the interface polarization as direct evidence of the electrical homogeneity. The magnitude of the breakdown strength (BDS) of the glass-ceramics is affected by the electrical homogeneity of the glass-ceramics. The average value of BDS is 1780 kV/cm for the Na2O–K2O–Nb2O5–SiO2–BaO glass-ceramics. The maximum potential energy storage density of 23.1 J/cm3 is obtained for the Na2O–K2O–Nb2O5–SiO2–BaO glass-ceramics with x = 3.