Structure, Phase Transition, and Electronic Properties of K_1−xNa_xNbO₃ Solid Solutions from First‐Principles Theory

Abstract

With extensive first-principles calculations, we investigated the geometric structure, phase transition, and electronic properties of orthorhombic, monoclinic, and tetragonal K 1x Na x NbO 3 (KNN) as functions of the Na content. We found that KNN undergoes an orthorhombic-to-monoclinic-to-orthorhombic phase transition when the Na content is gradually increased. We also found that the polarization vector of the monoclinic phase can be rotated more easily than those of the orthorhombic and tetragonal phases, giving rise to an enhanced piezoelectric response of the monoclinic KNN. Furthermore, our calculations provide an interpretation for the experimentally observed unusual broad peak of the KNN piezoelectric parameters.S. B. Sinnott-contributing editor Manuscript No. 35030.

Composition‐ and Pressure‐Induced Relaxor Ferroelectrics: First‐Principles Calculations and Landau‐Devonshire Theory

“…For the modeling of the complex (A,A')(B,B')O 3 solid solutions, we adopted the virtual crystal approximation in the primitive unit cells shown in Fig. , which implies preserving the same crystalline unit cells as the ternary compounds such as ABO 3 and replacing the metal A(B) with a virtual A'(B') atom . The cubic (C), tetragonal (T), rhombohedral (R), and orthorhombic (O) (A,A')(B,B')O 3 phases are kept with the Pm3m, P4mm, R3m, Amm2 symmetries, respectively, as shown in Fig.…”

“…[17][18][19][20][21] For the particular system of La-modified PbZr 0.65 Ti 0. 35 O 3 (PLZT x/65/35), the relaxor behavior in the dielectric response becomes experimentally discernible for La (x La ) concentrations above 6 at.%. 19 A newly discovered feature in the response of PLZT 6/65/35 is the observation of a spontaneous, first-order relaxor-to-normal ferroelectric transition on cooling and in the absence of a poling electric field.…”

Intrinsic origin of enhanced piezoelectricity in alkali niobate‐based lead‐free ceramics

“…In the poling process, all of the domains incline to gradually align along the direction of the external electric field, as shown in Figure A. However, the orthorhombic structures of KN and KNN have just 12 possible polarization directions, the <011> c pseudocubic directions . Hence, it cannot completely align along the direction of the external electric field.…”

“…However, the orthorhombic structures of KN and KNN have just 12 possible polarization directions, the <011> c pseudocubic directions. 34 Hence, it cannot completely align along the direction of the external electric field. However, it will possess the smallest possible angle θ between the polarization and external field.…”

Phase stability, electronic structures, and superconductivity properties of the BaPb1−xBixO3 and Ba1−xKxBiO3 perovskites

“…35,36 For modeling the BaPb 1Àx-Bi x O 3 and Ba 1Àx K x BiO 3 solid solutions in the range of 0≤x Bi(K) ≤0.5, we have adopted the VCA, which involves preserving the same crystalline unit cells as the ternary compounds such as BaPbO 3 (BaBiO 3 ) and replacing the metal Pb (Bi) with the virtual Bi (K) atom. 37 The crystal structures of the cubic (C), tetragonal (T), orthorhombic (O), and monoclinic (M) BPBO and BKBO phases are shown in Figure 1. A plane-wave cutoff energy of 400 eV was employed in the calculations, which assured a totalenergy convergence of 10 À6 eV/atom.…”