Special quasirandom structures to study the(K0.5Na0.5)NbO3random alloy

Abstract

The local structure of K0.5Na0.5NbO3 is investigated using first-principles methods with an optimized special quasirandom structure (SQS). Through a comparison of the computed pair distribution functions with those from neutron powder diffraction data, the SQS approach demonstrates its ability to accurately capture the local structure patterns derived from the random distribution of K and Na on the perovskite Asite. Using these structures, local variations in Na-O interactions are suggested to be the driving force behind the R3c to Pm phase transition. A comparison between the SQS and a rocksalt structure shows the inability of the latter to account for the local variability present in a random solid solution. As such, the predictive nature of the SQS demonstrated here suggests that this approach may provide insight in understanding the properties of a wide range of bulk oxide alloys or solid solutions. Disciplines Polymer and Organic Materials | Process Control and Systems | Structural Materials CommentsThis article is from Physical Review B 90 (2014) The local structure of K 0.5 Na 0.5 NbO 3 is investigated using first-principles methods with an optimized special quasirandom structure (SQS). Through a comparison of the computed pair distribution functions with those from neutron powder diffraction data, the SQS approach demonstrates its ability to accurately capture the local structure patterns derived from the random distribution of K and Na on the perovskite A-site. Using these structures, local variations in Na-O interactions are suggested to be the driving force behind the R3c to P m phase transition. A comparison between the SQS and a rocksalt structure shows the inability of the latter to account for the local variability present in a random solid solution. As such, the predictive nature of the SQS demonstrated here suggests that this approach may provide insight in understanding the properties of a wide range of bulk oxide alloys or solid solutions.

Coupling of emergent octahedral rotations to polarization in (K,Na)NbO3 ferroelectrics

“…These distortions, which relieve the tensile Na-O bond strain caused by the oversized [NaO 12 ] cages, result from Na displacements along the c -axis toward the O1 atoms (Fig. 2b), in accord with the theoretical predictions 28 . The magnitude of the Na off-centering in this direction, which is twice that of K, decreases from ≈0.26 Å for x  = 0.47 to ≈0.21 Å for both x  = 0.53 and x  = 0.58.…”

Non-conventional mechanism of ferroelectric fatigue via cation migration

“…To construct our supercell model we employed the special quasirandom structure (SQS) approach to define a random arrangement of cations 51 . Previously, we demonstrated that this approach was able to properly capture the atomic distortions present in a disordered, perovskite solid solution 52 . A Monkhorst Pack k -point grid of 2 × 2 × 2 was used for the Brillouin zone integration during structural optimization.…”

First principles materials design of novel functional oxides

“…For instance, using SQS it is possible to gain insights into the driving mechanisms behind the transition between the lowtemperature and high-temperature phases of the (K 1=2 Na 1=2 ) NbO 3 solid solution. 54 Additionally, predictions of phase stability point to potentially synthesizable regions of the Bi (Zn,Ti)O 3 -La(Zn,Ti)O 3 -PbTiO 3 phase diagram 34 (some of which have already been confirmed by experiment).…”

“…Recently, using the SQS approach we examined the high temperature (R3c) and low temperature (Pm) phases of the KNbO 3 -NaNbO 3 (KNO-NNO) solid solution. 54 Similar to PZT, KNO-NNO shows a significant enhancement in piezoelectric response at a composition near (K 0:5 Na 0:5 )NbO 3 (KNN) 55 and therefore has been considered to be an excellent starting structure for designing high-response, lead-free, electroceramics. [56][57][58] Given the relative chemical similarities between K and Na, it is anticipated that these cations will be distributed randomly on the perovskite A-site.…”