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Modeling porosity of high surface area nanopowders of the gallium nitride GaN semiconductor

机译:氮化镓GaN半导体高表面积纳米粉体的孔隙率建模

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A pool of high surface area gallium nitride GaN nanopowders was prepared and suitably characterized. The powders appeared to be mostly mesoporous with increasing share of microporosity at the highest surface area end. The BET surface area values spanned the range from 6.3 m~2 g~(-1) to 222 m~2 g~(-1) and specific mesopore volumes reached up to 0.21 cm~3 g~(-1). Powder XRD scans indicated for all samples the hexagonal polytype of GaN. Average crystallite sizes were calculated from the XRD data with Scherrer equation. Helium pycnometry was used to determine skeletal densities of the nanopowders in the wide range of 3.6-6.1 gcm~3. The densities showed an evident particle size dependence that could be explained by the presence of specific crystallite agglomerates impenetrable by helium atoms. Herein, a simple model of porosity for nanocrystalline powders, specifically nano-GaN, is proposed and confronted with the experimental data. The surface area for such nanopowders was modeled with appropriately specified surfaces of close-packed spheres (rigid and non-rigid configurations) as a function of sphere diameter. Selected model variants were statistically best-fitted with experimental data points, i.e., BET specific surface areas and average crystallite sizes determined from the XRD scans, to yield very good solutions. They support the view that the BET surface area of the GaN nanocrystalline powders basically corresponds with the accessible surface area of the nanoparticles - crystallites and/or agglomerates.
机译:制备了高表面积氮化镓GaN纳米粉池并进行了适当表征。粉末似乎大部分是中孔的,在最高表面积末端的微孔份额增加。 BET比表面积范围从6.3 m〜2 g〜(-1)到222 m〜2 g〜(-1),中孔比容达到0.21 cm〜3 g〜(-1)。粉末XRD扫描表明所有样品均为GaN的六方多晶型。使用谢勒方程,由XRD数据计算平均晶粒尺寸。氦比重瓶法用于测定纳米粉的骨架密度,范围为3.6-6.1 gcm〜3。密度显示出明显的粒度依赖性,这可由氦原子不可渗透的特定微晶团聚物的存在来解释。在此,提出了用于纳米晶体粉末,特别是纳米GaN的孔隙率的简单模型,并面对实验数据。这种纳米粉末的表面积是根据密实球体(刚性和非刚性构型)的适当指定的表面作为球体直径的函数进行建模的。所选模型变体在统计学上与实验数据点最匹配,即BET比表面积和XRD扫描确定的平均微晶尺寸,以产生非常好的溶液。他们支持以下观点:GaN纳米晶体粉末的BET表面积基本上与纳米颗粒(微晶和/或团聚体)的可及表面积相对应。

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