Structures and energetics of Ga2O3 polymorphs
Structures and energetics of Ga2O3 polymorphs
复制标题
DOI：
10.1088/0953-8984/19/34/346211
复制
发表时间：
2007-08-29
影响因子：
2.7
通讯作者：
Tanaka, I.
中科院分区：
文献类型：
--
作者：
Yoshioka, S.;Hayashi, H.;Tanaka, I.
第一性原理计算了五种Ga_2 O_3多晶型。空间群为Pna 2（1）（No.33，正交晶系）的ε-Ga 2 O 3的结构，在文献中有时称为kappa-Ga 2 O 3，与实验报告一致。γ-Ga_2 O_3的结构在有缺陷的尖晶石结构的14种不等价构型内得到优化。得到了四种多晶型的声子色散曲线。在准调和近似下，计算了体积膨胀率、体积弹性模量和定容比热随温度的变化关系。的亥姆霍兹自由能的多晶型物进行比较。膨胀率显示出β <α <δ的关系，而体积模量显示出β <α <δ <α的关系。在低温下，生成自由能有β <δ <γ <的趋势。随着温度的升高，β相和ε相之间的自由能差变小。最终e相在1600 K以上变得更稳定。
First-principles calculations are made for five Ga2O3 polymorphs. The structure of epsilon-Ga2O3 with the space group Pna2(1) (No. 33, orthorhombic), which is sometimes called kappa-Ga2O3 in the literature, is consistent with experimental reports. The structure of gamma-Ga2O3 is optimized within 14 inequivalent configurations of defective spinel structures. Phonon dispersion curves of four polymorphs are obtained. The volume expansivity, bulk modulus, and specific heat at constant volume are computed as a function of temperature within the quasi- harmonic approximation. The Helmholtz free energies of the polymorphs are thus compared. The expansivity shows a relationship of beta < epsilon < alpha < delta, while beta < epsilon < delta < alpha for the bulk modulus. The formation free energies have the tendency beta < epsilon < delta < gamma < at low temperatures. With the increase of temperature, the difference in free energy between the beta-phase and the epsilon-phase becomes smaller. Eventually the e phase becomes more stable at above 1600 K.