Hydrothermal synthesis of perovskite and pyrochlore powders of potassium tantalate

Goh, Gregory K. L.; Haile, Sossina M.; Levi, Carlos G.; Lange, F. F.

doi:10.1557/jmr.2002.0458

Cited by 80 publications

(78 citation statements)

References 29 publications

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“…This type of nonstoichiometry has been observed for hydrothermally synthesized BaTiO 3 and KTaO 3 powders and also for the KNbO 3 powders in this study. [40][41][42] As for H 2 O molecules, it was proposed in an earlier work that H 2 O molecules reside on vacant potassium sites, based primarily on the similarity in size of K and H 2 O. 42 The chemical formula of the as-synthesized potassium niobate hydrate may be written as K x Nb y O 3−z (OH) z · nH 2 O, where x + 5y + z ‫ס‬ 6 for charge neutrality.…”

Section: B Proton Incorporation and Removalmentioning

confidence: 99%

“…[40][41][42] As for H 2 O molecules, it was proposed in an earlier work that H 2 O molecules reside on vacant potassium sites, based primarily on the similarity in size of K and H 2 O. 42 The chemical formula of the as-synthesized potassium niobate hydrate may be written as K x Nb y O 3−z (OH) z · nH 2 O, where x + 5y + z ‫ס‬ 6 for charge neutrality. The dehydration reaction that occurs upon heating can, in turn, be written in terms of the overall change in stoichiometry, as shown in Reaction (5):…”

Section: B Proton Incorporation and Removalmentioning

confidence: 99%

“…42 This creates vacant sites (potassium and oxygen vacancies) for the subsequent diffusion of water molecules from beneath the surface. This process of vacancy creation proceeds inwards, analogous to a drying front, as water molecules diffuse to the surface.…”

Section: (Ohmentioning

confidence: 99%

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Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

et al. 2003

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Orthorhombic KNbO 3 and NaNbO 3 powders were hydrothermally synthesized in KOH and NaOH solutions (6.7-15 M) at 150 and 200°C. An intermediate hexaniobate species formed first before eventually converting to the perovskite phase. For synthesis in KOH solutions, the stability of the intermediate hexaniobate ion increased with decreasing KOH concentrations and temperatures. This led to significant variations in the induction periods and accounted for the large disparity in the mass of recovered powder for different processing parameters. It is also believed that protons were incorporated in the lattice of the as-synthesized KNbO 3 powders as water molecules and hydroxyl ions.

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Section: B Proton Incorporation and Removalmentioning

confidence: 99%

Section: B Proton Incorporation and Removalmentioning

confidence: 99%

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Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

et al. 2003

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“…Here, these rate limitations result into two different growth regimes: nucleation of stepped terraces and "smoothing" of the nanoparticle facets. SEM images taken in a STEM are capable of distinguishing between the two growth regimes by resolving these terraces.The KTO nanoparticles were made according to the synthesis developed by Goh et al, where Ta2O5 and a KOH solution are added to an autoclave and heated to 150 °C for different lengths of time between 1-4 hours [5]. Powder X-ray diffraction (XRD) was performed using a Rigaku DMAX diffractometer.…”

mentioning

confidence: 99%

“…The KTO nanoparticles were made according to the synthesis developed by Goh et al, where Ta2O5 and a KOH solution are added to an autoclave and heated to 150 °C for different lengths of time between 1-4 hours [5]. Powder X-ray diffraction (XRD) was performed using a Rigaku DMAX diffractometer.…”

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Growth Regimes of Hydrothermally Synthesized Potassium Tantalate Nanoparticles

Marks

2017

Microsc Microanal

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Nanoparticles have a broad range of applications, from increasing the efficiency of heterogeneous catalysis to creating the next generation energy storage devices. Hydrothermal synthesis is a popular technique because it yields highly pure, monodisperse nanoparticles spanning a wide range of chemical compounds, directly made possible due to the increased solubility of the reagents at elevated temperatures and pressures. Despite many studies modelling the growth thermodynamics and kinetics of colloidal nanoparticles, few exist for hydrothermally synthesized oxide nanoparticles [1,2]. Continuum methods, such as the kinetic and thermodynamic Wulff construction, predict the equilibrium nanoparticle shapes [3,4]. While popular for modelling oxide nanoparticles, these methods do not explain what is happening to the nanoparticles during growth.This study uses secondary electron (SE) imaging in a scanning transmission electron microscope (STEM) to study the kinetic growth of potassium tantalate (KTO) nanoparticles synthesized hydrothermally. In kinetic growth, the rate of growth is dependent on both the diffusion of atoms to a growing surface and the nucleation of a terrace on that growing surface [4]. Here, these rate limitations result into two different growth regimes: nucleation of stepped terraces and "smoothing" of the nanoparticle facets. SEM images taken in a STEM are capable of distinguishing between the two growth regimes by resolving these terraces.The KTO nanoparticles were made according to the synthesis developed by Goh et al., where Ta2O5 and a KOH solution are added to an autoclave and heated to 150 °C for different lengths of time between 1-4 hours [5]. Powder X-ray diffraction (XRD) was performed using a Rigaku DMAX diffractometer. A Hitachi HD-2300A STEM was used to characterize the product with the secondary electron detector. Figure 1 shows XRD patterns of the synthesis products after different lengths of time. Based on the observed diffraction peaks, the reactants are almost completely converted to KTO after 2 hours of synthesis time. SEM images of the cuboidal KTO nanoparticles after different synthesis times are shown in Figure 2. In Figures 2a-d, the observed nanoparticle facets are not completely flat and are instead populated with numerous terraces. After 2 hours of synthesis, the facets appear completely smooth (Figure 2e) and similar in appearance to the final product after 4 hours (Figure 2f). These stepped terraces exhibit the two different growth regimes of the KTO nanoparticles. As described above, the growth of nanoparticles is dependent on the nucleation of a terrace on an existing surface and the diffusion of atoms to that surface. A high rate of terrace nucleation will result in very rough facets, as observed in Figures 2a-d. The increasing smoothness from Figure 2a to Figure 2e suggests that the terrace nucleation rate is decreasing as the synthesis progresses. Furthermore, the dominating growth mechanism changes from terrace nucleation to facet "smoothing" at some point between 1 a...

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KTaO₃—The New Kid on the Spintronics Block

Gupta¹,

Harsha²,

Kumari³

et al. 2022

Advanced Materials

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Long after the heady days of high‐temperature superconductivity, the oxides came back into the limelight in 2004 with the discovery of the 2D electron gas (2DEG) in SrTiO3 (STO) and several heterostructures based on it. Not only do these materials exhibit interesting physics, but they have also opened up new vistas in oxide electronics and spintronics. However, much of the attention has recently shifted to KTaO3 (KTO), a material with all the “good” properties of STO (simple cubic structure, high mobility, etc.) but with the additional advantage of a much larger spin‐orbit coupling. In this state‐of‐the‐art review of the fascinating world of KTO, it is attempted to cover the remarkable progress made, particularly in the last five years. Certain unsolved issues are also indicated, while suggesting future research directions as well as potential applications. The range of physical phenomena associated with the 2DEG trapped at the interfaces of KTO‐based heterostructures include spin polarization, superconductivity, quantum oscillations in the magnetoresistance, spin‐polarized electron transport, persistent photocurrent, Rashba effect, topological Hall effect, and inverse Edelstein Effect. It is aimed to discuss, on a single platform, the various fabrication techniques, the exciting physical properties and future application possibilities of this family of materials.

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Hydrothermal synthesis of perovskite and pyrochlore powders of potassium tantalate

Cited by 80 publications

References 29 publications

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

Growth Regimes of Hydrothermally Synthesized Potassium Tantalate Nanoparticles

KTaO₃—The New Kid on the Spintronics Block

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Hydrothermal synthesis of perovskite and pyrochlore powders of potassium tantalate

Cited by 80 publications

References 29 publications

Hydrothermal synthesis of KNbO3 and NaNbO3 powders

Hydrothermal synthesis of KNbO3 and NaNbO3 powders

Growth Regimes of Hydrothermally Synthesized Potassium Tantalate Nanoparticles

KTaO3—The New Kid on the Spintronics Block

Contact Info

Product

Resources

About

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

KTaO₃—The New Kid on the Spintronics Block