CaO或BaO与Sm2O3共掺杂CeO2体系电子结构和氧离子迁移的DFT+U研究

使用GGA+U方法研究了Ca O或Ba O与Sm2O3共掺杂Ce O2体系几何和电子结构及氧离子迁移。计算结果表明,Ba和Sm均靠近氧空位时Ba Sm Ce30O63体系最稳定;Sm靠近,Ca远离氧空位时Ca Sm Ce30O63体系最稳定。Ba Sm Ce30O63和Ca Sm Ce30O63体系中均不存在Ce4+变价。对Ca Sm Ce30O63体系氧离子迁移的研究发现,当氧离子迁移到空位时,迁移能大小顺序为Em(3→V)Em(1→V)Em(4→V)Em(2→V),这一规律源于氧离子与低价掺杂离子产生负电势之间的排斥作用;对Ba Sm Ce30O63体系氧离子迁移的研究发现,当空位迁移到周围氧离子时,迁移能大小顺序为Em(V→3)Em(V→5)Em(V→1),这一规律源于氧空位产生的正电势与低价掺杂离子产生的负电势之间的吸引作用。此外,Ca Sm Ce30O63体系最小迁移能小于Sm Ce31O63体系,证实了Ce O2-Sm2O3-Ca O体系离子电导率大于Ce O2-Sm2O3体系的实验结果。     

Effects of Doping and Oxygen Vacancy Concentrations on Oxygen Ion Migration in Sm_xCe_(1-x)O_(2-δ): a DFT + U Study

Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy(V) migration energies of Sm_xCe_(1-x)O_(2-δ)(x = 0.0625, 0.125, 0.25 and δ = 0.0625, 0.125) systems using a GGA+U method are studied. Calculated results show that advantage migration types change from V?O~(2-) to O~(2-) ?V as x and δ increase. For V?O~(2-) migrations of the Sm_(0.0625)Ce_(0.9375)O_(1.9375) and Sm_(0.125)Ce_(0.875)O_(1.9375) systems, electrostatic attractions between Sm~(3+) and V, defect associations between Ce~(3+) and V, and steric hindrances of Sm~(3+) affect the migration energies. For O~(2-) ?V migrations of the Sm+(0.125)Ce_(0.875)O_(1.875) and Sm_(0.25)Ce_(0.75)O_(1.875) systems, migration energies of O~(~(2-) ) are affected by electrostatic repulsions between Sm~(3+) and O~(2-) and defect associations between Ce~(3+) and V. Increases of the oxygen vacancy and Sm~(3+) doping concentrations benefit the oxygen ion and vacancy migrations, respectively.     

CaO或BaO与Sm2O3共掺杂CeO2体系电子结构和氧离子迁移的DFT+U研究

使用GGA+U方法研究了CaO或BaO与Sm₂O₃共掺杂CeO₂体系几何和电子结构及氧离子迁移。计算结果表明,Ba和Sm均靠近氧空位时BaSmCe₃₀O₆₃体系最稳定;Sm靠近,Ca远离氧空位时CaSmCe₃₀O₆₃体系最稳定。BaSmCe₃₀O₆₃和CaSmCe₃₀O₆₃体系中均不存在Ce⁴⁺变价。对CaSmCe₃₀O₆₃体系氧离子迁移的研究发现,当氧离子迁移到空位时,迁移能大小顺序为E_m(3→V)< E_m(1→V)< E_m(4→V)< E_m(2→V),这一规律源于氧离子与低价掺杂离子产生负电势之间的排斥作用;对BaSmCe₃₀O₆₃体系氧离子迁移的研究发现,当空位迁移到周围氧离子时,迁移能大小顺序为E_m(V→3)< E_m(V→5)< E_m(V→1),这一规律源于氧空位产生的正电势与低价掺杂离子产生的负电势之间的吸引作用。此外,CaSmCe₃₀O₆₃体系最小迁移能小于SmCe₃₁O₆₃体系,证实了CeO₂-Sm₂O₃-CaO体系离子电导率大于CeO₂-Sm₂O₃体系的实验结果。     

基于曲率和电子结构的掺杂C50和C70富勒烯的稳定性研究

使用密度泛函理论(DFT)-B3LYP/6-31G^*方法研究了B、N、Si、P和Co在C₅₀和C₇₀中的掺杂能和电子结构, 并基于曲率理论和电子结构探讨了掺杂富勒烯的结构稳定性. 计算结果表明, 掺杂能随着原子曲率的增大而减小, 随着掺杂物种原子半径的增大而增大, B、N、P和Co的掺杂有利于C₅₀结构的稳定, 而B和N的掺杂不利于C₇₀结构的稳定; 除了用于反映原子活性的曲率主要决定掺杂反应性, 各不等价碳原子在C₅₀和C₇₀的最高占据分子轨道(HOMO)中所占成分对掺杂能的影响也很大, 且其成分越大越有利于掺杂. 此外, 掺杂原子得失电子情况与其电负性有关. 本工作将为富勒烯结构稳定性的研究提供理论依据.     

Transitional Area of Ce~(4+) to Ce~(3+) in Sm_xCa_yCe_(1-x-y)O_(2-δ) with Various Doping and Oxygen Vacancy Concentrations: A GGA + U Study

In this work,we perform DFT+U periodic calculations to study geometrical and electronic structures and oxygen vacancy formation energies of Sm_xCa_yCe_(1-x-y)O_(2-δ)systems(x=0.0312,0.0625,0.125 and 0.250;y=0.0312,0.0625,0.125 and 0.250;δ=0.0312,0.0625,0.125,0.250 and 0.50)with different oxygen vacancy and doping concentrations.The calculated results show that the V_1-Sm~(3+)-V_2 structures where there is a position relationship of the face diagonal between V_1 and V_2 both nearest to Sm~(3+)have the lowest energy configurations.The study on electronic structures of the Sm_xCa_yCe_(1-x-y)O_(2-δ)systems finds that excess electrons arise from oxygen vacancies and are localized on f-level traps of their neighbor Ce,and Ca~(2+)and Sm~(3+)co-doping effectively restrains the reduction of Ce~(4+).In order to avoid the existence of Ce~(3+),x and y must be both larger than 0.0625 asδ=0.125 orδmust be smaller than 0.125 as x=y=0.0625.The Ce~(3+)/Ce~(4+)change ratio k has an obvious monotonous increase with increasing the vacancy oxygen concentration.The introduction of Sm~(3+)decreases k.In addition,the doped Sm~(3+)can restrain the reduction of Ce~(4+)when the V_1-Sm~(3+)-V_2 structure with a face diagonal position relationship in lower reduced atmosphere exists.It need be pointed out that the Sm_(0.25)Ce_(0.75)O_(1.5) system should be thought of as a Sm-doped Ce_2O_3 one.