Electrical and structural characterization of (K_xNa_1−x)NbO₃ceramics modified with Li and Ta

Abstract

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.

Structural phase transitions and electrical properties of (K Na1−)NbO3-based ceramics modified with Mn

“…The piezoelectric coefficient of the samples obtained from the slope of the unipolar strain hysteresis curves show that low d * 33 values are obtained compared to when there is no Mn present. 9 …”

“…Mn appears to have very little effect on the phase coexistence of the KNNLiTa-2Mn sample because the sequence and temperature of the phase transitions are similar with and without it. 9 Composition fluctuation which in a way is due to compositional inhomogeneities is believed to be the main reason for phase coexistence in the samples. 36 The change in slope of the lattice parameters observed at certain temperatures for the samples correspond to a phase transition.…”

“…When used in their optimum amounts to dope KNN ceramics, Sb, 3 Li, 4,5 Ta 6 alone or in combination [7][8][9][10][11] have all been reported to improve the piezoelectric properties. * Corresponding author.…”

Effect of Ti on the properties of (KxNa1−x)NbO3 based lead-free ceramics

“…Doping of KNN ceramics with isovalent elements is known to result in higher piezoelectric properties compared to the undoped sample [3,[6][7][8][9]. This is mostly associated with the lowering of the temperature of the tetragonal phase leading to a two-phase coexistence near room temperatures [10]. In the case of aliovalent doping, the effect of the dopant on the properties of KNN ceramics can vary.…”

Investigation of the phase space in lead-free (K x Na1-x )1-y Li y (Nb1-z Ta z )O3 ferroelectric ceramics

“…The addition of high amounts of Li + and Ta 5+ to KNN induces a phase transformation from an orthorhombic phase to a tetragonal phase. Between the two phases is a two-phase boundary which is a combination of both orthorhombic and tetragonal phases and has been reported [27,28]. This two-phase boundary was initially reported as an MPB just like in PZT [29], but further investigations show that the piezoelectric properties depend strongly on temperature and so the term "polymorphic phase boundary" is more appropriate.…”