Local structure and phase transitions of KNbO₃

Abstract

Bond length distributions of nearest- and higher-neighbor distances in KNbO3, which is the parent compound of lead-free piezoelectric materials, have been obtained by X-ray pair-distribution function (PDF) analysis. The Rietveld analysis of high-energy powder X-ray diffraction data as a function of temperature from 15 to 1073 K over four phases shows the variation in structure from rhombohedral to cubic structures. The refinements on the local structure by the PDF method indicate that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion is maintained locally in all four phases.

Polar metals in strain-engineered KNbO3/CaNbO3 superlattices: a first-principles study

“…For the tetragonal KNO, our calculated lattice constants are a = 4.008 Å and c = 4.109 Å, close to the experimental values of a = 3.995 Å and c = 4.046 Å. 25 And the electric polarization value is 0.354 C m −2 , in good accordance with the reported theoretical value of 0.35 C m −2 and the experimental value of 0.37 C m −2 . 32,33 The electronic densities of states (DOSs) show an insulating nature with a band gap of 1.32 eV.…”

“…As is known, KNO undergoes a series of transformations from the cubic phase to the tetragonal phase, then to the orthorhombic phase, and finally to the rhombohedral phase when cooling from high temperatures. 25 Except for the first phase which is paraelectric, the last three phases are ferroelectric with the spontaneous polarizations along the [001], [110], and [111] directions, respectively. For CNO, only the Pnma phase with an a À a À c + oxygen octahedral rotation mode is considered.…”

Short- and middle-range order structures of KNbO3 nanocrystals

“…Then, we tried the fit using a rhombohedral structure model, which can reproduce the short-range order structure of bulk KNbO 3 . [30][31][32][33] The result of fitting is shown in Fig. 3(c).…”

Studies of Optical, Dielectric, Ferroelectric, and Structural Phase Transitions in 0.9[KNbO3]-0.1 [BaNi1/2Nb1/2O3−δ]

“…Recently, the influence of such lattice modes on the phase stability in other oxides such as Sr 2 ZnGe 2 O 7 [46] and BaTe 2 O 6 [47] have been reported. In fact, the sequence of phase transition in KNbO 3 resulted from lattice deformation and the distortion in the NbO 6 octahedra [48].…”