Cook Daniel S, Hooper Joseph E, Dawson Daniel M, Fisher Janet M, Thompsett David, Ashbrook Sharon E, Walton Richard I
Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
School of Chemistry, EaStCHEM and Centre of Magnetic Resonance, University of St Andrews, North Haugh, St Andrews KY16 9ST, U.K.
Inorg Chem. 2020 Mar 16;59(6):3805-3816. doi: 10.1021/acs.inorgchem.9b03459. Epub 2020 Feb 24.
The synthesis of a new solid solution of the oxyhydroxide GaAlO(OH) is investigated via solvothermal reaction between gallium acetylacetonate and aluminum isopropoxide in 1,4-butanediol at 240 °C. A limited compositional range of 0 ≤ ≤ 1.5 is produced, with the hexagonal unit cell parameters refined from powder X-ray diffraction (XRD) showing a linear contraction in unit cell volume with an increase in Al content. Solid-state Al and Ga nuclear magnetic resonance (NMR) spectroscopies show a strong preference for Ga to occupy the tetrahedral sites and Al to occupy the octahedral sites. Using isopropanol as the solvent, γ-GaAlO defect spinel solid solutions with ≤ 1.8 can be prepared at 240 °C in 24 h. These materials are nanocrystalline, as evidenced by their broad diffraction profiles; however, the refined cubic lattice parameter shows a linear relationship with the Ga:Al content, and solid-state NMR spectroscopy again shows a preference for Al to occupy the octahedral sites. Thermal decomposition of GaAlO(OH) occurs via poorly ordered materials that resemble ε-GaAlO and κ-GaAlO, but γ-GaAlO transforms above 750 °C to monoclinic β-GaAlO for 0 ≤ ≤ 1.3 and to hexagonal α-GaAlO for = 1.8, with intermediate compositions of 1.3 < < 1.8 giving mixtures of the α- and β-polymorphs. Solid-state NMR spectroscopy shows only the expected octahedral Al for α-GaAlO, and for β-GaAlO, the ∼1:2 tetrahedral:octahedral Al ratio is in good agreement with the results of Rietveld analysis of the average structures against powder XRD data. Relative energies calculated by periodic density functional theory confirm that there is an ∼5.2 kJ mol penalty for tetrahedral rather than octahedral Al in GaAlO(OH), whereas this penalty is much smaller (∼2.0 kJ mol) for β-GaAlO, in good qualitative agreement with the experimental NMR spectra.
通过乙酰丙酮镓与异丙醇铝在1,4 - 丁二醇中于240°C下进行溶剂热反应，研究了新型羟基氧化物GaAlO(OH)固溶体的合成。生成了0≤ ≤1.5的有限组成范围，通过粉末X射线衍射（XRD）精修的六方晶胞参数显示，随着Al含量的增加，晶胞体积呈线性收缩。固态Al和Ga核磁共振（NMR）光谱表明，Ga强烈倾向于占据四面体位置，而Al倾向于占据八面体位置。以异丙醇为溶剂，在240°C下24小时内可制备出 ≤1.8的γ - GaAlO缺陷尖晶石固溶体。这些材料为纳米晶，其宽衍射图谱证明了这一点；然而，精修的立方晶格参数与Ga:Al含量呈线性关系，固态NMR光谱再次表明Al倾向于占据八面体位置。GaAlO(OH)的热分解通过类似于ε - GaAlO和κ - GaAlO的无序材料发生，但对于0≤ ≤1.3，γ - GaAlO在750°C以上转变为单斜β - GaAlO，对于 = 1.8则转变为六方α - GaAlO，1.3 < < 1.8的中间组成给出α - 和β - 多晶型的混合物。固态NMR光谱显示，对于α - GaAlO仅观察到预期的八面体Al，对于β - GaAlO，四面体:八面体Al的比例约为1:2，这与根据粉末XRD数据对平均结构进行Rietveld分析的结果高度吻合。通过周期性密度泛函理论计算的相对能量证实，在GaAlO(OH)中四面体Al相对于八面体Al存在约5.2 kJ/mol的能量罚值，而对于β - GaAlO，该罚值要小得多（约2.0 kJ/mol），这与实验NMR光谱在定性上高度一致。
