The effects of iron as a dopant on the dielectric properties of ferroelectric potassium tantalate niobate (KTaxNb1−xO3)

Abstract

Presented here is a preliminary study on the effects of iron as a dopant in potassium tantalate niobate (KTaxNb1−xO3) (KTN). Crystals of high purity were grown using a top-seeded isothermal method with starting materials that were purified ensuring that the impurity content was controlled down to less than 10ppm. The study included introducing iron to KTN single crystals of high purity both during crystal growth and through thermal diffusion after growth. Dielectric measurements versus temperature were used to reveal the origins of the ferroelectric phase transition in the KTN:Fe system. Large shifts in the Curie temperature have been shown to be a direct consequence of the presence of iron impurities in KTN. The conventional theories of ferroelectricity do not explain this effect; however, a model is proposed to explain the observed behavior. The model is based on the concept of “polar microregions” proposed previously by Bidault and Maglione [J. Phys. I France 7, 543 (1997)] and others to explain ferroelectricity in potassium tantalate lightly doped with niobium.

Structure and Piezoelectric Properties of Fe-Doped Potassium Sodium Niobate Tantalate Lead-Free Ceramics

“…The increase of the lattice parameters may suggest that Fe 3+ ions occupy K and Na vacancies, originating from the volatilization of alkali metal elements, because too many vacancies will result in lattice collapse. This variation of the lattice parameters is similar to the case of Fe‐doped LiNbO 3 , it might indicate that at low doping concentration of Fe 2 O 3 , the Fe 3+ ions fill in the vacancies induced by the volatilization of alkaline element, occupying the A sites, lead to lattice parameters increase; while at high doping concentration of Fe 2 O 3 , the Fe ions replace Nb, Ta ions due to similar ionic radius, occupying the B sites and lead to lattice parameters decrease 24,25 …”

“…We assume that the majority of the Fe ions in the compound are trivalent due to the oxidizing conditions in the air during all the preparing process. This has been confirmed by electron paramagnetic resonance on Fe‐doped KTN, 24,25,30 however, the sites where Fe 3+ ions occupy is not very clear 25–28,31,32 . Regarding this matter, E. Possenriede et al 30 concluded that Fe 3+ (0.064 nm) ions in KTN system occupy Nb 5+ (0.069 nm) and Ta 5+ (0.068 nm) sites.…”

“…When the concentration of Fe 2 O 3 exceeds 0.6 mol%, these parameters decrease rapidly due to the high dielectric loss. Y. M. Abdulraheem et al 25 have pointed out that in KTN crystal, the enhancement in dielectric loss was caused by the increase of dipolar entities inside the sample after the diffusion of Fe 3+ . However, the details of the dopant mechanism are still unknown.…”

“…It is well known that Fe element is widely used to enhance properties in crystal 24–28 . In this work, ferric oxide (Fe 2 O 3 ) was added into K 0.5 Na 0.5 Nb 0.95 Ta 0.05 O 3 (abbreviated as KNNT5) ceramics to improve the sintering characters and their piezoelectric properties.…”

Ferroelectric Phase Transition in Cu-doped BaTiO3 Crystals

“…A broadening and flattening of the maximum of ε(T) and a shift of the Curie temperature T c have also been observed in Fe-doped BaTiO 3 ceramics [10,11]. Similar effects also exist in the potassium tantalite niobate [12] and in several oxides with perovskite structure: Nb:KTaO 3 , Cu,La:PbTiO 3 [13]. After annealing at 1300K for 150 hours, there is a loss of copper (% Cu becomes: y~0.55x) and temperature T m increases in Cu:BaTiO 3 crystals (Fig.…”