Grain-boundary sliding in high-temperature ceramics: mechanical spectroscopy of high-purity magnesium oxide

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The demise of elastic behaviour in materials stressed at sufficiently high temperature limits the usefulness of ceramics for structural applications, and is also responsible for reduced wave speeds and associated attenuation of seismic waves in the Earth's interior. Yet the nature of the transition in fine-grained materials tested at high temperature from elastic through anelastic to viscous rheology remains poorly understood. Through a combination of mechanical testing by torsional forced oscillation/ microcreep methods of carefully fabricated and characterised specimens of polycrystalline MgO and associated micro-mechanical modelling we seek to clarify this fundamental and general aspect of high-temperature mechanical behaviour.