Crucial Role of Water in the Mechanosynthesis of CsPbI3 and Other ABX3 Halides

Mechanochemical synthesis of CsPbI₃, as a model system for ABX₃ halides, was studied. Water was shown to strongly promote the kinetics of formation of CsPbI₃ from the CsI+PbI₂ mixture through increased mobility of the constituting ionic species. Since many binary and ternary halides are hygroscopic, it was concluded that the presence of small, uncontrollable and unintentional additions of water should often occur in both precursor mixtures and synthesized complex halides boosting the kinetics of formation of many, if not all, ternary organic–inorganic hybrid halides such as, for example, MAPbX₃ (X=Cl, Br, I). In addition, trace amounts of water should influence the transport characteristics of complex halides. Thus, the presence of water explains, at least partially, the huge scatter in both the reported mechanochemical reaction times necessary for obtaining single-phase APbX₃ perovskite halides and the activation energies of ionic diffusion in APbX₃.     

A class of 2-generator subgroups of PSL (2, C)

Dedicated to Yuri Grigor'evich Reshetnyak on his sixtieth birthday     

Gaussian effective potential and symmetry restoration at high temperatures in four-dimensionalO(N)×O(N) field theory

The phase structure of theO(N)×O(N) scalar theory (1) has been studied in the Gaussian potential approximation. It has been shown that at a zero temperature a spontaneous breaking of symmetry is possible. At sufficiently largeT theO(N)×O(N) invariance of the model is restored.     

Approximation of functions of two variables by harmonic splines

We construct two-dimensional splines and give two versions of an estimate of the deviation of splines from approximated functions. We compare approximations by a planar broken line and by a harmonic spline. We also substantiate the advisability of introduction of the notion of harmonic splines in mathematics.Deceased.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 9, pp. 1190–1196, September, 1995.     

Interdiffusion in two-layer Pd/Ag films I. The effects of interphase boundaries

Interdiffusion processes in epitaxial single-crystal Pd/Ag thin films within the temperature range 20°–500°C are studied by transmission electron microscopy, electron diffraction and electrical resistance methods. Homogenization is investigated both during deposition and during annealing.The mass transfer kinetics is found to depend significantly on the original structure of the interphase boundary (dislocations present or not) and on its reconstruction due to interdiffusion. Regular networks of misfit dislocations at the interface can retard interdiffusion, while network failures lead to acceleration of homogenization process. The vacancy flows play a decisive role in these processes. The effects of interphase dislocations on the DIGM, DIR and RID processes are discussed.The numerical study of electrical resistance variations during annealing is carried out. The concentration profiles are plotted for a nontrivial dependence of interdiffusion coefficient on concentration. The numerical results are compared with the experimental data.     

New critical properties of the Nambu-Jona-Lasinio model with nonzero chemical potential

It is shown for the first time that the massive-fermion state in the Nambu-Jona-Lasinio model with nonzero chemical potential μ is described by two different phases, the transition between which is second-order. It is proved that both first-and second-order phase transitions, depending on the values of the model parameters, restore the chiral symmetry of the model. Two tricritical points exist in the (μ, M) phase diagram (M is the dynamical fermion mass at μ=0). Zh. éksp. Teor. Fiz. 111, 1921–1934 (June 1997)