Structure, dielectric, and energy storage behaviors of the lossy glass-ceramics obtained from Na₂O-Nb₂O₅-P₂O₅ glassy-system

ABSTRACT

A series of phosphate glasses defined by the composition 50Na₂O-xNb₂O₅-(50-x)P₂O₅ (0<x < 25 mol%) and designated as Nb5, Nb10, Nb15, Nb20, Nb25, respectively, have been elaborated by the melt quenching method, and their structural and optical properties were investigated. It was found that their density and molar volume increase and decrease with the Nb₂O₅ content, respectively. The analysis of the glasses structure by Raman spectroscopy allowed the identification of several phosphate structural units, mainly metaphosphate and pyrophosphate, and showed that niobium adopts an octahedral oxygen environment, forming linkages such as Nb-O-P and Nb-O-Nb within the network. Glass-ceramics were obtained by controlled heat treatments of the parent glasses. The heat treatment of the high niobium concentration glass Nb25 at 650°C led to the formation of the sodium niobate phase with cubic symmetry. Its microstructure was analyzed by SEM. The study of the dielectric properties of the glass-ceramics and their energy storage performance presented an optimum discharge density for the glass-ceramic with 25 mol% Nb₂O₅ and an energy efficiency of 82.5%.

KEYWORDS:

• Phosphate glasses
• glass-ceramics
• crystallization
• NaNbO₃
• dielectric properties
• energy storage behavior

Acknowledgment

This work was supported by Centre National pour la Recherche Scientifique et Technique: [grant number Mat-Bih01/2017]; OCP Foundation: [grant number Mat-Bih-01/2017]. F.M and F.R-M gratefully acknowledge the support of the AEI (Spanish Government) Projects (Nos. MAT2017-87035-C2-1-P and MAT2017-86450-C4-1-R). F.R.-M. is indebted to MINECO for the ‘Ramon y Cajal’ contract (ref: RyC-2015-18626), which is co-financed by the European Social Fund. F.R.-M. also acknowledges support from a 2018 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Centre National pour la Recherche Scientifique et Technique: [grant number Mat-Bih01/2017]; OCP Foundation: [grant number Mat-Bih-01/2017].