Hot Pressing of Potassium‐Sodium Niobates

TLDR

These potassium‑sodium niobates lack pyroplastic behavior, requiring temperatures near those used for air sintering. Hot‑pressing yielded >99 % dense ceramics with finer microstructure, higher piezoelectric and radial coupling coefficients (up to ~48 %), increased dielectric constants, and retained high ac losses, making equimolar compositions attractive for 10–20 MHz electromechanical transducers, and the process follows the Murray–Live–Williams rate equation.

Abstract

Compositions in the system KNbO 3 ‐NaNbO 2 have been hot‐pressed to yield ceramics with relative densities greater than 99%. Because these materials lack any degree of pyroplastic behavior, temperatures approaching those required for air sintering are needed. These hot‐pressed specimens exhibit a finer microstructure than that obtainable by conventional processing. Enhanced piezoelectric coefficients are observed, and in certain compositional regions radial coupling coefficients have been increased from 32 to approximately 48%. Dielectric constants increase with densification and ac losses remain relatively high. The fine structure and improved piezoelectric activity, especially near the equimolar composition, make these materials desirable for electromechanical transducers, particularly in the 10 to 20 Mc per second range. The rate equation of Murray, Live, and Williams for hot‐pressing ceramics was found to apply in this system.