Hydrothermal synthesis of single-crystal α-tristrontium phosphate particles

Anisotropic ceramic bodies can be fabricated by a reactive template grain growth method; however, template particles with suitable powder properties are required to create the ceramics with well controlled anisotropy. Therefore, we synthesized well-isolated α-tristrontium phosphate (α-TSP) particles with a hexagonal plate-like shape as template particles for anisotropic strontium apatite ceramics using α-strontium hydrogen phosphate (α-SrHPO₄) precursor particles. Three synthetic parameters were varied: (i) precursor particle size, (ii) stirring rate, and (iii) hydrothermal temperature. Well-isolated hexagonal plate-like α-TSP single-crystal particles were successfully synthesized by hydrothermal treatment at 150 °C for 3 h at a stirring rate of 150 rpm using fine α-SrHPO₄ precursor particles. The developed plane of the hexagonal plate-like α-TSP particles was determined to be the {00l} plane, and the side planes were revealed to be not {h00} planes, but inclined {h0l} planes. The resulting α-TSP particles may provide a promising template for the development of anisotropic apatite-based ceramics.     

Complement to “Optical and Judd-Ofelt spectroscopic study of Er3+-doped strontium gadolinium gallium garnet single-crystal”

In the previous paper “Optical and Judd-Ofelt spectroscopic study of Er³⁺-doped strontium gadolinium gallium garnet single-crystal” (J Am Ceram Soc. 2019;102:873–878), we have reported optical and Judd-Ofelt spectroscopic properties of Er³⁺-doped strontium gadolinium gallate (SrGdGa₃O₇) single-crystal, and the Judd-Ofelt study was performed on the basis of unpolarized absorption spectrum of the crystal. Present work reports the corrected unpolarized absorption spectrum and Er³⁺ concentration in the crystal, and hence corrected Judd-Ofelt spectroscopic properties and cross-section data. In addition, the polarization effect was considered in the Judd-Ofelt analysis on the basis of polarization-resolved absorption spectra. Effective Judd-Ofelt parameters are presented and discussed in comparison with the results from the unpolarized spectrum, and consistent results have been obtained. This study also considers the effects of some other factors on the Judd-Ofelt parameters. These include Er³⁺ concentration and selection of Er³⁺ absorption bands for the Judd-Ofelt analysis.     

Preparation of excessively Ni2+-exchanged zeolite Y (FAU,Si/Al = 1.70) and its single-crystal structure

A single crystal of excessively Ni²⁺-exchanged zeolite Y (FAU, Si/Al = 1.70) was prepared by exchange of |Na₇₁|[Si₁₂₁Al₇₁O₃₈₄]-FAU with an aqueous stream 0.05 M Ni(NO₃)₂ at 293 K and pH 4.9, followed by vacuum evacuation at room temperature and 1.3 × 10^?4 Pa. Its crystal structure was determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m and was refined to the final error indices R ₁/wR ₂ = 0.0554/0.1557 for |Ni_24.7(NiOH)_12.1(Ni₂O(OH)₂)_4.8(Ni₄AlO₄)_1.7Na_17.0(H₃O)_6.9|[Si₁₁₇Al₇₅O₃₈₄]-FAU. Crystal has about 53 Ni²⁺ ions per unit cell, indicating the uptake of excess Ni(OH)₂, perhaps as NiOH⁺ ions. Some dealumination of the framework occurred during Ni²⁺ exchange. In this structure, Ni²⁺ ions occupy sites I, I′, II′, II, and III′. The residual Na⁺ ions are found at sites II′ and II. Due to the low pH of the Ni²⁺ exchange solution, some H₃O⁺ ions are observed. Nonframework oxygen atoms as oxide and hydroxide ions and orthoaluminate coordinate to some of Ni²⁺ ions to give NiOH⁺, Ni₂O(OH)₂, and Ni₄AlO₄ ³⁺ groups.     

Effect of Tb3+ doping and self-generated pressure on the crystallographic/morphological features and thermal stability of LaPO4·nH2O single-crystal nanorods obtained by microwave-assisted hydrothermal synthesis

The effect of Tb³⁺-doping content (in the range 0–20 mol%) and autogeneous/self-generated pressure (in the range 2.3–3.4±0.1 bar) on the crystallographic/morphological features and thermal stability of single-crystal nanorods of LaPO₄·nH₂O obtained by a simple and fast microwave-assisted hydrothermal synthesis was investigated. It is shown that high-quality (that is, well-shaped and linear/planar defect free) rhabdophane-type single-crystal La_1-xTb_xPO₄·nH₂O (x=0–0.20) nanorods, with a high morphological uniformity, are obtained in all cases. In addition, it is shown that the Tb³⁺ solutes are incorporated into the LaPO₄·nH₂O host, forming substitutional solid solutions (i.e., partial substitution of La³⁺ by Tb³⁺) with progressively smaller unit-cell volume but with identical thermal stability. Morphologically Tb³⁺ doping however results in the formation of nanorods with lower aspect ratio. With respect to the self-generated pressure during the microwave synthesis, it is shown that its increase does not affect to crystallographic aspects, but however results again in nanorods with lower aspect ratio. It is also demonstrated that monazite-type single-crystal La_1-xTb_xPO₄ nanorods can be obtained by calcining their rhabdophane-type La_1-xTb_xPO₄·nH₂O counterparts at ~700 °C in air. Consequently, in the present study important guidelines have been identified for the controlled synthesis of functional La_1-xTb_xPO₄·nH₂O nanorods with tailored morphology.     

Synthesis of plate-like α-Al2O3 single-crystal particles in NaCl–KCl flux using Al(OH)3 powders as starting materials

Plate-like α-Al₂O₃ single-crystal particles were successfully synthesized in NaCl–KCl flux using Al(OH)₃ powders as starting materials, and the influence of pre-calcining of Al(OH)₃ powders on the phase formation and morphology of α-Al₂O₃ powders was focused. When Al(OH)₃ powders are used as starting materials, the synthesized product at 900 °C is mainly composed of α-Al₂O₃ and κ-Al₂O₃, and most synthesized particles show alveolate morphology. At 1100 °C, single-phase α-Al₂O₃ powders are developed, in which there are many aggregations of intensively bound plate-like particles. In contrast, using porous amorphous Al₂O₃ powders obtained by pre-calcining Al(OH)₃ powders at 550 °C for 3 h as the starting material, plate-like α-Al₂O₃ single-crystal particles can be well developed above 900 °C. The reason of the influence of pre-calcining of Al(OH)₃ powders on the phase formation and morphology of α-Al₂O₃ powders is also discussed in the paper.     

Behavior of cesium cation in zeolite Y (FAU,Si/Al = 1.56) and their single-crystal structures, |Cs<Subscript>75−x</Subscript>Na<Subscript>x</Subscript>|[Si<Subscript>117</Subscript>Al<Subscript>75</Subscript>O<Subscript>384</Subscript>]-FAU (x = 35 and 54)

To study the tendency of Cs⁺ exchange into zeolite Y (Si/Al = 1.56) dependence on Cs⁺ and Na⁺ concentration of aqueous solution during exchange, two single-crystals of fully dehydrated, Cs⁺-and Na⁺-exchanged zeolites Y were prepared by the flow method using a mixed ion-exchange solution whose CsNO₃:NaNO₃ mol ratios were 1:1 (crystal 1) and 1:100 (crystal 2), respectively, with a total concentration of 0.1 M, followed by vacuum dehydration at 723 K. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.084/0.248 and 0.088/0.274 for crystals 1 and 2, respectively. In the structure of |Cs₄₀Na₃₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 1), 40 Cs⁺ ions per unit cell occupy five different equipoints; 3, 3, 14, 9, and 11 are at sites I, II′, II, IIIa and IIIb, respectively, whereas, the remaining 35 Na⁺ ions occupy three different sites: 9, 11, and 15 are at sites I, I′, and II, respectively. In the structure of |Cs₂₁Na₅₄|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 2), 21 Cs ⁺ ions per unit cell occupy three equipoints; 4, 6, and 11 are at sites II, IIIa, and IIIb, respectively. The residual 54 Na⁺ ions per unit cell are found at three different sites; 6, 20 and 28 are at sites I, I′, and II, respectively. The degrees of ion exchange are 53 and 28 % for crystals 1and 2, respectively. This result shows that the degree of Cs⁺ exchange decreased sharply by decreasing the initial Cs⁺ concentration and increasing the initial Na⁺ concentration in given ion-exchange solution.