Kinetic Growth Regimes of Hydrothermally Synthesized Potassium Tantalate Nanoparticles

Abstract

A general mathematical kinetic growth model is proposed on the basis of observed growth regimes of hydrothermally synthesized KTaO nanoparticles from electron microscopy studies on the surface morphology and surface chemistry. Secondary electron imaging demonstrated that there are two dominant growth mechanisms: terrace nucleation, where the surfaces are rough, and terrace growth, where surfaces are smooth. In the proposed model based upon standard step-flow growth, the rates of both mechanisms are established to be dependent on the chemical potential change of the growth environment-terrace nucleation dominates with larger negative chemical potential, and terrace growth dominates with smaller negative chemical potential. This analysis illustrates the importance of ending a synthesis in a regime of low negative chemical potential in order to achieve smooth well-faceted nanoparticles.

Direct Observation of Large Flexoelectric Bending at the Nanoscale in Lanthanide Scandates

“…These values are in agreement with previously reported values , and help explain the large charging: the band gap and work function of DyScO 3 are approximately equal, so almost every secondary electron produced by inelastic scattering in the bulk has sufficient energy to escape the material. As a direct confirmation of this hypothesis, Figure compares secondary electron images of GdScO 3 and KTaO 3 nanoparticles. , As can be seen in this image, the GdScO 3 nanoparticles have less topographic contrast than the KTaO 3 nanoparticles, and a significantly lower secondary electron signal except near the conducting carbon support or KTaO 3 nanoparticles. The lack of topographic contrast directly indicates a long mean free path of the electrons; the lower secondary electron signal is because the GdScO 3 has charged significantly more positive than the KTaO 3.…”

“…As a direct confirmation of this hypothesis, Figure 3 compares secondary electron images of GdScO 3 and KTaO 3 nanoparticles. 38,39 As can be seen in this image, the GdScO 3 nanoparticles have less topographic contrast than the KTaO 3 nanoparticles, and a significantly lower secondary electron signal except near the conducting carbon support or KTaO 3 nanoparticles. The lack of topographic contrast directly indicates a long mean free path of the electrons; the lower secondary electron signal is because the GdScO 3 has charged significantly more positive than the KTaO 3.…”

Complex Fluorine Chemical Potential Effects on the Shape and Compositional Heterogeneity of KTa1–xNbxO3 Nanoparticles

“…The nanocuboids shown in Figure 2 were typical of particles grown at lower KF/KOH concentrations, and their morphologies matched the nucleation and growth via surface terraces behavior studied previously. 15,16 In contrast to the nanocuboids, anisotropically shaped particles also formed at higher concentrations of KF (KF/KOH > 0.20). These particles were flat rectangular flakes on the order of several hundred nanometers wide and ∼100 nm thick (Figure 3), and EDS maps of these particles shown in Figure S1 did not demonstrate any significant composition segregation as the cuboidal KTN particles did.…”

Controlled Two-Step Formation of Faceted Perovskite Rare-Earth Scandate Nanoparticles

“…SE imaging of REScO 3 (RE = La, Nd, Sm, Gd) particles (Figure 4) confirmed that these conditions led to smaller and better faceted particles, as the GdScO 3 particles produced with the two-step heat treatment (Figure 4) were more faceted than those produced with only a single nucleation step (Figure 2). Increasing the nucleation temperature further would likely increase the nucleation rate and reduce particle size [35]. In addition, the small particulates found in the one-step samples were no longer present in the two-step heat treatment.…”

“…There are advantages to approaching the problem as one of nucleation and growth instead. In a recent analysis of the growth of KTaO 3 nanoparticles [35], it was determined that the growth process could be subdivided into two regimes, one with a high chemical potential difference where terrace nucleation and rough-stepped surfaces dominated, and one with a lower chemical potential difference where step-flow growth annihilated steps to smooth surfaces. This analysis leads to predictions regarding which parameters need to be varied to control the nucleation and growth processes, ultimately tuning the conditions to produce particles with specific shapes or sizes.…”