Lead free ferroelectric ceramics of the KNN-LiTaO 3 -LiSbO 3 system were prepared using the (from ≈9500 to <6000). At temperatures below 300 •C however, the loss tangent in the doped samples (≈2.5 mol%) was much lower and steady when compared to the undoped one. The ferroelectric properties were slightly lowered with the addition of MnO2. The remnant polarisation (Pr) was lowered from ~18µC/cm2 to ~9µC/cm2, the coercive field (E c ) from ~ 8.5 kV/cm to ~ 6.2 kV/cm and the piezoelectric charge coefficient (d 33 ) decreased as well.

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SynopsisThe effect of Li + and Ta 5+ on the crystal structure and electrical properties of (K x Na 1-x )NbO 3 ceramics has been investigated. Abstract (K x Na 1-x )NbO 3 ceramics modified with Li + and Ta 5+ have been produced using the mixed-oxide synthesis method. Synchrotron X-ray diffraction measurements were made on the samples from 12K to temperatures above their ferroelectric-paraelectric transition points with 10K measurement steps. Rietveld refinement using FULLPROF suite was used to refine the patterns. Depending on the composition and temperature, rhomhohedral phases, orthorhombic phases, tetragonal phases, cubic phases and two-phase mixtures were obtained.R3c (161), Amm2 (38), P4mm (99), m Pm3 (221) space groups and their combinations were used to refine the rhombohedral, orthorhombic, tetragonal, cubic and the mixed phases respectively. Li + addition suppressed the formation of the rhombohedral low temperature phase and increased the Curie temperature. This is attributed to size difference in ionic radii of the A-site elements which leads to increased atomic polarizability and increased interaction with the B-site element. Li + and Ta 5+ co-doping led to a wide temperature range of phase coexistence between the orthorhombic and tetragonal phase. Electrical characterizations by dielectric and hysteresis measurements were used to compare with the results from the structural studies.

Abstract

The effect of high doping levels of manganese (Mn) on the structure and electrical properties of (KxNa1−x)NbO3 (KNN) ceramics containing Li, Ta, and Sb has been investigated. The samples were measured using synchrotron X‐ray diffraction whereas Rietveld refinement with Fullprof was used to determine the structural information as a function of temperature. Temperature‐dependent dielectric measurement was used to compare the phase transition temperatures. The results show that Mn decreases the temperature range of phase coexistence between the orthorhombic and tetragonal phase from ~180°C to ~120°C. The Curie temperature remained unchanged with Mn addition while the dielectric constant and dielectric loss increased with Mn addition. High amounts of Mn led to a reduction in both piezoelectric and ferroelectric properties. The remnant polarization, remnant strain, and piezoelectric coefficient values decreased from 24 μC/cm2, 0.000824, 338 ± 37 pm/V to 13 μC/cm2, 0,00014 and 208 ± 27 pm/V, respectively for the undoped and 5 mol% Mn‐doped sample.