Electrochemical studies on lead iodide

The total d.c. electrical conductivity of undoped PbI₂ was measured as a function of iodine potential in the region 150–300°C to determine the nature of charge carriers in PbI₂. Results indicate that PbI₂ is an ionic conductor with electron holes as the minority carriers in this temperature range. Electrical polarization experiments were also performed to determine the electron hole conductivity and concentrations, mobilities and chemical diffusion coefficients of electron holes in undoped PbI₂ between 150 and 300°C.     

Phase transformations in disordered alloys of composition close to Fe3Pt

The phase transformations in disordered Fe₃Pt alloys with decrease in temperature are studied by x-ray structural analysis. Two simultaneous transformations are observed: an incomplete martensitic structural phase transition of the first kind and a -type intraphase (-phase) transformation. The martensitic transformation in Fe₃Pt alloy is preceded by the appearance of a singular pretransformational state in the -phase, in which the behavior of the fine-structure parameter differs from that in the initial state of this phase.Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Tomsk State Architectural and Building Academy. Translated from Izvestiya Vysshikh Uchebnykh Zavednii, Fizika, No. 4, pp. 83–88, April, 1994.     

蒸发条件对碘化铅多晶薄膜结构的影响

采用真空蒸发法在普通玻璃上制备了PbI₂多晶薄膜.研究了蒸发速率、蒸发源与衬底距离、薄膜厚度以及衬底温度等实验条件对所制备PbI₂多晶薄膜结构的影响.利用X射线衍射仪和扫描电子显微镜对样品进行了测试.结果表明，在衬底温度为室温时得到(001)择优取向的多晶PbI₂薄膜，即沿c轴垂直衬底方向取向生长的薄膜.当衬底温度升高时，薄膜的择优取向逐渐由(001)转向(003)，且晶体颗粒变大.薄膜中的内应力随衬底温度的升高而降低.     

Phase transformations of the magnetic structure in film nanobridges

The magnetic structure of a plane nanobridge consisting of two ferromagnetic film electrodes connected by a nanosized crossbar of the same material is studied. Due to their magnetoresistive properties, such bridges are of considerable interest for microelectronics. Using a numerical micromagnetics method, it is shown that a domain wall is displaced from the center of the bridge crossbar as the anisotropy constant of the system decreases and reaches a critical value. A phase diagram is constructed, which makes it possible to determine the possible magnetic states of real nanobridges. The mechanism of the phase transformation is described in terms of an analytical model. This model explains the shape of the phase diagram of the nanobridge. Formally, the transformations of the magnetic structure of the nanocontact can be described in terms of the Landau theory of phase transitions in a certain range of parameters of the system.     

Photostimulated desorption studies on potassium iodide

Abstract

In this work we present the results of photostimulated desorption measurements obtained on KI under excitation in the fundamental absorption region. Yield curves of both potassium and iodine desorbed atoms are reported at several sample temperatures. We discuss the experimental results in terms of the optical constants and of the production efficiency of F and H centers in KI.     

Phase transformations of a condensate on a crystal surface in a strong electric field

The evolution of the phase state of the water vapor condensate of the silver iodide crystal surface in an applied electric field up to 10 V/nm is studied by computer simulation. The previously found domain structure of the contact layer is stable against the external field and remains up to the complete break of the molecular film. In a strong electric field, the film condensation mode is changed by the formation of a new phase consisting of molecular nanothreads growing in the direction of the electric field lines. The transition to the new state is sharp. The presence of a phase transition is likely analogous to that accompanying the transformation of water microdrops to the superpolarized state under the action of an external electric field at stratospheric temperatures.     

First-principles study on optic-electronic properties of doped formamidinium lead iodide perovskite

We have discussed the materials of solar cell based on hybrid organic–inorganic halide perovskites with formamidinium(NH_2CH = NH_2~+or FA) lead iodide. Firstly, we build the structure of formamidinium lead iodide(FAPbI_3) by using the material studio. By using the first-principles calculations, the energy band structure, density of states(DOS), and partial DOS(PDOS) of the hydrazine-iodide lead halide are obtained. Then, we theoretically analyze a design scheme for perovskite solar cell materials, published in [Science 354, 861(2016)], with the photoelectric conversion efficiency that can reach 20.3%. Also, we use non-toxic elements to replace lead in FAPbI_3 without affecting its photoelectric conversion efficiency. Here in this work, we explore the energy band structure, lattice constant, light absorption efficiency, etc. After the Ca, Zn, Ge Sr, Sn, and Ta atoms replacing lead(Pb) and through comparing the spectral distributions of the solar spectrum, it can be found that FAGeI_3, FASnI_3, and FAZnI_3 have better absorbance characteristics in the solar spectrum range. If the band gap structure is taken into account, FAGeI_3 will become an ideal material to replace FAPbI_3, although its performance is slightly lower than that of FAPbI_3. The toxicity of Pb is taken into account, and the Ge element can be used as a substitute element for Pb. Furthermore, we explore one of the perovskite materials, i.e., FA0.75Cs_(0.25)Sn_(0.25)Ge_(0.75)I_3 whose photovoltaic properties are close to those of FA_(0.75)Cs_(0.25)Sn_(0.5)Pb_(0.5)I_3, but the former does not contain toxic atoms.Our results pave the way for further investigating the applications of these materials in relevant technologies.     

一维无序体系电子跳跃导电研究

建立了电子隧穿电导模型,推导了一维无序体系新的直流电导公式.通过计算20000格点无序体系的直流电导率,分析了直流电导率和温度及外场电压的关系,讨论了无序度对直流电导的影响.计算结果表明,无序体系的直流电导率随无序度的增加而减小;外加电场较小时,电导率相对较大,且出现一系列峰值,电压较大时,电导率反而较小;无序体系在低温区出现了负微分电阻特性,电导率随温度的升高而增大,在高温区电导率随温度的升高而减小.计算结果和实验符合很好 关键词： 无序体系 电子隧穿 直流电导率     

Phase transformations in iron-boron carbide powder mixture and the structure of the sintered materials

The transformations at the phase interface in an iron-boron carbide powder mixture have been studied in the temperature range 1050–1200C. Their character is analyzed in the paper and data are given about the structure and phase composition of the sintered materials.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 77–83, September, 1977.     

Ground-state structure in a highly disordered spin-glass model

We propose a new Ising spin-glass model on Z ^d of Edwards-Anderson type, but with highly disordered coupling magnitudes, in which a greedy algorithm for producing ground states is exact. We find that the procedure for determining (infinite-volume) ground states for this model can be related to invasion percolation with the number of ground states identified as 2 ^N , whereN=N(d) is the number of distinct global components in the invasion forest. We prove thatN(d)= if the invasion connectivity function is square summable. We argue that the critical dimension separatingN=1 andN= isd _c=8. WhenN(d)=, we consider free or periodic boundary conditions on cubes of side lengthL and show that frustration leads to chaoticL dependence withall pairs of ground states occurring as subsequence limits. We briefly discuss applications of our results to random walk problems on rugged landscapes.     

Freezing of fluids confined in a disordered nanoporous structure

Freezing of a simple fluid in a disordered nanoporous carbon is studied using molecular simulations. Only partial crystallization occurs, and the confined phase is composed of crystalline and amorphous nanodomains. This freezing behavior departs strongly from that for nanopores of simple geometry. We present a method for analyzing the freezing in such disordered materials in terms of a transition in the average size and number of crystalline clusters. The results provide a basis for the interpretation of experiments on freezing in such materials, particularly 1H-NMR and scattering experiments.     

Self-diffusion at grain boundaries with a disordered atomic structure

A change in the free energy of a grain boundary is analyzed in the case when lattice vacancies come to the boundary and are then delocalized in its disordered atomic structure. It is shown that the free energy of the boundary is minimized at some excess atomic volume Δv _b =Δv _b ^* , whose value depends on the energy of vacancy formation in the crystal lattice and the boundary energy. The formation of a metastable localized grain-boundary vacancy as a result of thermal fluctuations of the density in a group of n ₀=\gM_v/Δv _b atoms (\gM_v is the vacancy volume), followed by the jump of an adjacent atom into this vacancy, is taken as an elementary event of grain-boundary diffusion. Expressions for the activation energy of diffusion and the diffusion coefficient are derived for equilibrium (Δv _b =Δv _b ^* ) and nonequilibrium (Δv _b >Δv _b ^* ) boundaries.     

Flexible X‐ray detector based on sliced lead iodide crystal

A promising flexible X‐ray detector based on inorganic semiconductor PbI₂ crystal is reported. The sliced crystals mechanically cleaved from an as‐grown PbI₂ crystal act as the absorber directly converting the impinging X‐ray photons to electron hole pairs. Due to the ductile feature of the PbI₂ crystal, the detector can be operated under a highly curved state with the strain on the top surface up to 1.03% and still maintaining effective detection performance. The stable photocurrent and fast response were obtained with the detector repeated bending to a strain of 1.03% for 100 cycles. This work presents an approach for developing efficient and cost‐effective PbI₂‐based flexible X‐ray detector.

     

On the theory of wannier exciton in a disordered structure

The motion of the optically excited coulomb-bounded electron-hole pair in a random gaussian potential has been investigated by using the Feynman path integral method. The motion of the mass center shows the same hopping character as a single particle. The coupling of the mass center motion and of the internal motion of the pair depends on the difference of the effective masses; ifm _e =m _h or ifm _e ?m _h the coupling tends to zero. A characteristic function \(F(\omega ) = \left( {1 - \frac{{\omega _c^2 }}{{2\omega ^2 }}\frac{{\phi \hbar \beta }}{{tg\frac{{\phi \hbar \beta }}{2}}}} \right)^{ - 1} \) has been found which determines the influence of the disorder on the internal motion of the pair. IfF(ω)→ 0 the motion is hydrogen-like, ifF(ω)→∞ the pair dissociates. The conditions for dominancy of the localizing influence of the random field or of the hydrogenlike motion due to the coulombic bound has been found. It has been shown that at high temperatures one can speak about the Wannier exciton at the same sense as in periodic lattices.     

Electronic structure of disordered BCC alloys

This paper describes and analyses a self-consistent cluster coherent potential approximation calculation of the electron density of states of a random, binary alloy on abcc lattice.