双层钙钛矿氧化物Sr_(2)CrBO_(6)(B=Os,Re,W)电子结构和光学性质的第一性原理研究

First-principles study on electronic structures and optical properties of double perovskites Sr_(2)CrBO_(6)(B=Os,Re,W)

Sr_(2)CrBO_(6)(B=Os,Re,W)被证实是具有最高磁转变温度的双钙钛矿氧化物.论文采用基于密度泛函理论的第一性原理方法,计算了Sr_(2)CrBO_(6)的电子结构和光学性质,并通过计算结果分析了二者之间的内在关系.总体来看,B位元素的改变对材料的电子结构和光学性质都产生了较大的影响.由能带结构的计算,Sr_(2)CrOsO_(6)为半导体,Sr_(2)CrReO_(6)和Sr_(2)CrWO_(6)为半金属.晶体介电函数虚部ε_(2)(ω)曲线在所考察的能量范围内存在明显的介电特征峰,论文结合态密度和能带结构讨论了这些介电峰所对应的电子跃迁过程.Sr_(2)CrOsO_(6)和Sr_(2)CrReO_(6)在可见光区域均有较强的吸收,其中,Sr_(2)CrReO_(6)在394 nm处的峰值吸收系数为38.54×10^(4)cm^(-1),Sr_(2)CrOsO_(6)在594 nm处的峰值吸收系数为29.11×10^(4)cm^(-1).根据反射率的计算,三种材料在可见光区域的反射率都小于0.3,反射损失较小.另外,Sr_(2)CrOsO_(6)和Sr_(2)CrReO_(6)虽然为单轴晶体,但其光学性质在所考察的能量范围内几乎是各向同性的.此研究为Sr_(2)CrBO_(6)(B=Os,Re,W)在光电子器件领域的应用提供了理论指导.

Sr_(2)CrBO_(6)(B=Os,Re,W)are the top three in the class of double perovskites which were measured to have the highest magnetic ordering temperature.In this work,we investigated the electronic structures and optical properties of Sr_(2)CrBO_(6) by using the first-principles method based on the density functional theory,and analyzed the internal relations between them.Overall,the change of B-site element has great influences on the electronic structures and optical properties.From the energy band structures,Sr_(2)CrOsO_(6) is a semiconductor,while Sr_(2)CrReO_(6) and Sr_(2)CrWO_(6) are half metals.The imaginary partsε_(2)(ω)of the complex dielectric functions of Sr_(2)CrBO_(6) all have obvious dielectric peaks within the considered energy region,then we discussed the corresponding electron transition processes from the density of states and energy band structures.Both Sr_(2)CrOsO_(6) and Sr_(2)CrReO_(6) have strong absorption in the visible light region.The peak absorption coefficients are 38.54×10^(4)cm^(-1)at 394 nm for Sr_(2)CrReO_(6) and 29.11×10^(4)cm^(-1)at 594 nm for Sr_(2)CrOsO_(6).The reflectivities of the three materials are all smaller than 0.3 in the visible light region,so the reflection loss is small.In addition,although Sr_(2)CrOsO_(6)and Sr_(2)CrReO_(6)are uniaxial crystals,their optical properties are almost isotropy within the considered energy region.Our results provide theoretical guidances for the applications of Sr_(2)CrBO_(6)(B=Os,Re,W)in the field of optoelectronic devices.