NiO敏感陶瓷的缺陷化学与导电机理

本文对 NiO 单晶及不掺杂和掺 Li,Al 的 NiO 陶瓷的高温(800～1400℃)电导率和温差电势进行了测量。在一定温度下,NiO 单晶的电导率与 P_(O_2)(?)成比例,不掺杂和掺 Al 的 NiO 陶瓷的电导率与 P_(O_2)(?)成比例,高温主缺陷为V″_(N(?)O)掺0.1mol%Li_2O 的 NiO 陶瓷的电导率,在低氧分压下,不随温度和氧分压而变化,由此计算出空穴迁移率μ为0.43cm~2/Vs。掺 Al 的 NiO 陶瓷在 P_(O_2)=10~5Pa,T>1200℃下的电导表观活化能为102.6kJ/mol。Ni_(1-(?))O 的非化学计量偏离量δ=7.75×10~(-2)exp(-16200/RT)。试验结果表明,采用电子空穴的宽能带传导机理比小极化子跃迁传导机理能较好地阐明塞贝克(温差电势)系数的温度关系。     

高施主掺杂 BaTiO_3 陶瓷中施、受主杂质相互作用的一种异常现象

在高施主掺杂 BaTiO_3陶瓷中,若引入适量的受主杂质,其室温电阻率测量结果显示出一种异常现象。本文用缺陷化学的理论,在施主、受主掺杂 BaTiO_3室温电阻率和平衡电导率测置的实验基础上,对受主杂质的异常作用提出了解释。在高施主掺杂 BaTiO_3陶瓷中,由单电离施主(F~(?))与单电离或双电离钡缺位(V′_(Ba)、V″_(Ba))之间的缔合形成了大量的复合缺陷。复合缺陷的浓度随受主杂质的引入而下降,这是引起上述异常现象的根源。在单一点缺陷模型中引入复合缺陷后,可使施、受主杂质对电导率异常影响的解释统一于一个理论模型中,从而使有关 PTC 效应的理论比过去获得更广泛的实验现象的验证。     

稀土发光材料Y2-x-yEuxLiyO3电荷补偿机制和发光机理研究

通过Li离子和发光离子共掺杂制备的稀土发光材料可以较大的提高样品的发光强度,本文通过密度泛函计算讨论这种材料中的电荷补偿形式,认为在较大浓度的情况下,对Li离子的电荷补偿主要以单独的间隙氧缺陷为主,间隙氧离子的引入,将会导致材料中出现掺杂能级。此外,基于试验结果,还对发光增强的机理进一步进行了讨论。     

Sr掺杂量对La1-xSrxMnO3-σ离子导电性能的影响

本文从La1-xSrxMnO3-σ,材料的缺陷结构出发,探讨了材料在高温条件下离子(氧离子)导电的形成机制.分析了Sr掺杂量对氧离子导电性的影响,发现当Sr掺杂量x＝O.5时,由La1-xSrxMnO3-σ材料的离子电导率达到最大,因为在这一掺杂浓度时,材料中形成了最佳的氧空(氧离子)传输通道.     

Sr掺杂量对La_(1-x)Sr_xMnO_(3-δ)离子导电性能的影响

本文从La1 -xSrxMnO3-δ材料的缺陷结构出发 ,探讨了材料在高温条件下离子 (氧离子 )导电的形成机制。分析了Sr掺杂量对氧离子导电性的影响 ,发现当Sr掺杂量x =0 .5时 ,La1 -xSrxMnO3-δ材料的离子电导率达到最大 ,因为在这一掺杂浓度时 ,材料中形成了最佳的氧空 (氧离子 )传输通道。     

(Y2O3,Yb2O3)复合掺杂ZrO2材料的中低温电导率

采用交流复阻抗体技术对（Y2O3，Yb2O3)复合掺杂ZrO2材料在573－873K这一温度范围的离子电导率随组成的变化关系进行了研究，发现在ZrO2-Y2O3系统加入Yb2O3会使得材料在中低温区域电导率降低。用经典的Arrhenius公式对实验数据进行的分析表明，导导率降低的原因在于Yb^3＋与结构中氧空位之间的缔合比Y^3 与氧空位之间的缔合更甚，阻碍了氧空位在中低温下的定向迁移。     

缺陷对RRAM材料阻变机理的影响

基于密度泛函理论(DFT)的第一性原理和VASP仿真软件,分析了阻变随机存储器(RRAM)阻变效应的物理机制。对比计算了单斜晶相HfO2中Ag掺杂体系、氧空位缺陷体系和Ag及氧空位缺陷共掺杂复合缺陷体系的能带、态密度、分波电荷态密度面和形成能,结果表明在相同浓度下Ag掺杂体系能形成导电通道,而氧空位缺陷体系不能形成导电通道;共掺杂体系中其阻变机制以Ag传导为主,氧空位缺陷为辅,且其形成能变小,体系更加稳定。计算共掺杂体系的布居数和迁移势垒,得出在氧空位缺陷存在的前提下,Ag—O键长明显增加,Ag离子的迁移势垒变小,电化学性能增强。进一步计算了缺陷间的相互作用能,其值为负,表明缺陷间具有相互缔合作用,体系更加稳定。     

ZrO2掺杂BaCo0.7Fe0.2Nb0.1O3-δ材料的高温结构稳定性和电学性能

为了制备ZrO2掺杂的BaCo0.7Fe0.2Nb0.1O3-δ(BCFN)样品并研究其高温化学稳定性和电学性能,分别通过XRD研究了材料相成分的变化;通过收缩率和密度的测量并结合SEM研究了材料的微观结构;通过TG实验研究了材料在一定气氛下随温度的失重变化;通过直流四电极法测量了材料总电导的变化规律.研究结果表明,BCFN掺杂ZrO2之后材料为双相复合结构.随着ZrO2掺杂量的增加,材料在惰性气氛和氢气气氛下表现出更好的结构稳定性.ZrO2掺杂与未掺杂的BCFN体系其电学性能随温度的变化规律相同,在570℃之前的低温范围以P型半导体电子空穴导电机制为主,在高温则是同时存在电子空穴导电与氧离子导电,随着ZrO2掺杂量的增加,材料在空气气氛下的总电导率依次下降.     

ZnO薄膜p型掺杂的研究进展

ZnO是一种新型的II-VI族半导体材料,具有许多优异的性能.但由于ZnO存在诸多的本征施主缺陷(如空位氧V_o和间隙锌Zn_i),对受主产生高度自补偿作用,天然为n型半导体,难以实现p型转变.ZnO薄膜p型掺杂的实现是ZnO基光电器件的关键技术,也一直是ZnO研究中的主要课题,目前已取得重大进展,文章对此进行了详细阐述.     

HfO_2中间隙氧缺陷特性第一性原理研究

运用第一性原理计算研究了HfO2中间隙氧缺陷的特性。对HfO2中不同位置的间隙氧缺陷的形成能进行了计算,找出了最稳定的间隙氧缺陷位置,并对该位置缺陷计算了缺陷能级、态密度(DOS)和电荷俘获能;另外,还计算了间隙氧缺陷之间的距离对HfO2性质的影响。计算结果显示间隙氧缺陷能够同时俘获电子和空穴,具有两性特征;俘获的电荷主要聚集在间隙氧和最近邻氧原子附近;间隙氧之间距离增大会使得缺陷之间由吸引变为排斥,排斥力随距离继续增大而减小,并且缺陷引入的受主能级量子态数显著增加,这有利于空穴隧穿电流增大,可以用来实现存储层电荷的快速擦除。     

高阻In掺杂CdZnTe晶体缺陷能级的研究

利用低压垂直布里奇曼法制备了不同In掺杂量的CdZnTe晶体样品, 采用低温光致发光谱(PL)、深能级瞬态谱(DLTS)以及霍尔测试等手段研究了In掺杂CdZnTe晶体中的主要缺陷能级及其可能存在的补偿机制. PL测试结果表明, 在In掺杂样品中, In原子占据了晶体中原有的Cd空位, 形成了能级位于E_c-18meV的替代浅施主缺陷[In_Cd^+], 同时 [In_Cd⁺]还与[V_Cd^2-]形成了能级位于E_v+163meV的复合缺陷[(In_Cd⁺-V_Cd^2-)^-]. DLTS分析表明, 掺In样品中存在导带以下约0.74eV的深能级电子陷阱能级, 这个能级很可能是Te反位[Te_Cd]施主缺陷造成的. 由此, In掺杂CdZnTe晶体的电学性质是In掺杂施主缺陷、Te反位深能级施主缺陷与本征受主缺陷Cd空位和残余受主杂质缺陷补偿的综合结果.     

Nb掺杂Bi4Ti3O12层状结构铁电陶瓷的电行为特性研究

采用固相烧结工艺制备了Nb5+掺杂的Bi4Ti3O12层状结构铁电陶瓷.运用XRD和AFM对Bi4Ti3-xNbxO12+x/2材料的微观结构进行表征,发现所制备的陶瓷均具有单一的正交相结构,抛光热腐蚀表面晶粒的显微形貌表现为随机排列的棒状结构.通过对材料直流电导率与温度关系的Arrhenius拟合,分析了Bi4Ti3-xNbxO12+x/2的导电机理.Nb5+掺杂提高了材料的介电常数,但居里温度随掺杂含量的增加呈线性下降趋势.DSC结果显示Bi4Ti3-xNbxO12+x/2材料在居里温度处经历了一级铁电相变.样品的铁电性能测试结果表明,Nb5+掺杂Bi4Ti3O12提高了材料的剩余极化Pr,这主要是由于Nb5+取代Ti4+大大降低了材料中氧空位的浓度,使得氧空位对畴的钉扎作用减弱的缘故.     

ZnGeP2晶体点缺陷的研究进展

ZnGeP₂晶体是具有重要应用背景的红外非线性光学材料. 晶体中的点缺陷严重限制了ZnGeP₂晶体的应用发展. 本工作介绍了ZnGeP₂晶体点缺陷的最新研究进展情况. 首先, 利用电子顺磁共振技术研究了ZnGeP₂晶体的点缺陷. 主要存在缺陷是受主缺陷V^-_Zn及施主缺陷V⁰_P和Ge⁺_Zn, 其相应的缺陷能级分别为E(V^-_Zn)=E_C-(1.02±0.03)eV, E(V⁰_P)=E_V+(1.61±0.06)eV和E(Ge⁺_Zn)=E_V+(1.70±0.03)eV. 对晶体作了电子照射及高温退火等处理后, 又分别发现了两种缺陷V ^3-_Ge和VPi. 其次, 利用全势能线性muffin-tin轨道组合法模拟研究了ZnGeP₂晶体的点缺陷. 主要存在缺陷及缺陷能级的计算结果与实验结果基本一致, 但由于理论模拟与实际情况还存在差距, 有些计算结果与实验结果相矛盾. 因此, 将实验与理论有机结合研究晶体的点缺陷是今后研究的重点.     

Point defects in ZnO: an approach from first principles

Abstract

Recent first-principles studies of point defects in ZnO are reviewed with a focus on native defects. Key properties of defects, such as formation energies, donor and acceptor levels, optical transition energies, migration energies and atomic and electronic structure, have been evaluated using various approaches including the local density approximation (LDA) and generalized gradient approximation (GGA) to DFT, LDA+U/GGA+U, hybrid Hartree–Fock density functionals, sX and GW approximation. Results significantly depend on the approximation to exchange correlation, the simulation models for defects and the post-processes to correct shortcomings of the approximation and models. The choice of a proper approach is, therefore, crucial for reliable theoretical predictions. First-principles studies have provided an insight into the energetics and atomic and electronic structures of native point defects and impurities and defect-induced properties of ZnO. Native defects that are relevant to the n-type conductivity and the non-stoichiometry toward the O-deficient side in reduced ZnO have been debated. It is suggested that the O vacancy is responsible for the non-stoichiometry because of its low formation energy under O-poor chemical potential conditions. However, the O vacancy is a very deep donor and cannot be a major source of carrier electrons. The Zn interstitial and anti-site are shallow donors, but these defects are unlikely to form at a high concentration in n-type ZnO under thermal equilibrium. Therefore, the n-type conductivity is attributed to other sources such as residual impurities including H impurities with several atomic configurations, a metastable shallow donor state of the O vacancy, and defect complexes involving the Zn interstitial. Among the native acceptor-type defects, the Zn vacancy is dominant. It is a deep acceptor and cannot produce a high concentration of holes. The O interstitial and anti-site are high in formation energy and/or are electrically inactive and, hence, are unlikely to play essential roles in electrical properties. Overall defect energetics suggests a preference for the native donor-type defects over acceptor-type defects in ZnO. The O vacancy, Zn interstitial and Zn anti-site have very low formation energies when the Fermi level is low. Therefore, these defects are expected to be sources of a strong hole compensation in p-type ZnO. For the n-type doping, the compensation of carrier electrons by the native acceptor-type defects can be mostly suppressed when O-poor chemical potential conditions, i.e. low O partial pressure conditions, are chosen during crystal growth and/or doping.     

Electrical conductivity in Ta2O5

The defect structure of undoped polycrystalline Ta₂O₅ was investigated by determining the temperature [850–1050°C] and oxygen partial pressure [10⁰–10^?19 atm.] dependence of the electrical conductivity. The data were found to be proportional to the $\text{～?}\text{1}\text{4}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range <10^?8 atm. and independent of the oxygen partial pressure for P_O2 > 10^?6 atm. The enthalpy of formation of doubly ionized oxygen vacancies plus two electrons is estimated to be 118.31 Kcal/mole [5.13 eV]. The observed conductivity data are explained on the basis of the presence of unknown acceptor impurities in the undoped samples.     

La9(SiO4)6-x(VO4)xO1.5+0.5x的合成及其导电性能的研究

利用溶胶-凝胶法低温合成了钒掺杂硅酸盐氧基磷灰石La9(SiO4)6-x(VO4)xO1.5+0.5x(x=0、0.5和1),经XRD表征所得产品为磷灰石相.以电化学阻抗谱研究了其导电性能,V的掺杂使电导率大大提高,700℃时La9(SiO4)5(VO4)O2电导率为5.23×10-3S·cm-1,与未掺杂V的La9(SiO4)6O1.5相比提高了5倍.氧分压Po2=105～1Pa时,La9(SiO4)6O1.5的电导率不改变,而La9(SiO4)5(VO4)O2的电导率则随着氧分压的降低而稍有增加,表明钒的掺杂在体系中引入n型电子导电.     

Defect structure of acceptor-doped calcium titanate at elevated temperatures

The defect structure of acceptor (Al or Cr)-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure dependence (at 10° to 10–18 atm) of the electrical conductivity at 1000 and 1050° C. The observed electrical conductivity data were proportional to for the oxygen pressure range < 10^–10 atm and proportional to for the oxygen pressure range ( 10^–7 atm. The conductivity values were observed to increase with the acceptor concentration in the p-type region with the shift in the conductivity minima towards lower oxygen partial pressure. The absolute value of the electrical conductivity in the acceptor-doped samples were lower in the n-type region compared to the values in the undoped CaTiO₃. Aluminium and chromium were found to be equally effective in acting as acceptor impurities in CaTiO₃. The defect chemistry of CaTiO₃ is dominated by the added acceptor impurities for the entire oxygen partial pressure range used in this investigation.     

Semiconducting and transport properties of mono- and polycrystalline nickel oxide

On the basis of high-temperature studies of electrical conductivity of poly- and monocrystalline nickel oxide and making use of the results of studies on chemical diffusion coefficients obtained by several authors and in the present work, the structure of point defects in nickel oxide has been considered. It has been shown that in the temperature range 900 to 1300° C and at the oxygen pressure from 10^–4 to 1 atm there occur in nickel oxide singly- and doubly-ionized cationic vacancies in comparable quantities.Assuming such to be the model of defect structure in Ni_1–yO, the equilibrium concentration of cationic vacancies as a function of temperature has been calculated for the oxygen pressure of 1 atm. It has been shown that the results obtained are in good agreement with the results of direct determinations of concentration of cationic vacancies in NiO.     

AC conduction in amorphous thin films of SnO<Subscript>2</Subscript>

Alternating current (a.c.) electrical properties of thermally evaporated amorphous thin films of SnO₂ sandwiched between aluminium electrodes have been investigated for temperature during electrical measurements, film thickness, substrate temperature and post-deposition annealing. The a.c. conductivity, σ(ω), is found to vary with frequency according to the relation σ(ω) ∝ ω^s, indicating a hopping process at low temperature. The conduction is explained by single polaron hopping process as proposed by Elliott. The increase in electrical conductivity with increase in temperature during electrical measurements is ascribed to the increase in the formation and high mobility of doubly ionized oxygen vacancies. The increase in conductivity with increase in film thickness is caused by the increase in interstitial tin, oxygen vacancies and defects produced due to deviation from stoichiometry. The increase in conductivity with increase in substrate and annealing temperature may be due to the formation of singly or doubly ionized oxygen vacancies and tin species of lower oxidation state. Measurements of capacitance C as a function of frequency and temperature show a decrease in C with increasing frequency and increase in C with increasing temperature. The increase in capacitance in the high-temperature low-frequency region is probably due to space charge polarization induced by the increasing number of free carriers as a result of increasing temperature.     

Influence de la pression partielle d'oxygene sur la nature des defauts ponctuels dans Ca2LaFe3O8+x

The type of point defects in non-stoichiometric Ca₂LaFe₃O_8+x ferrite has been studied by measuring the variation of electrical conductivity with oxygen partial pressure at various temperatures. Several ordering possibilities occur. The oxygen atoms inserted, mostly 1-charged, have a strong tendency to couple at sufficient oxygen pressure and at low temperature. Interstitial oxygen atoms in the lattice vacancies induce structural evolution as non-stoichiometry becomes significant enough.