Optical constants of Cu2ZnSnS4 thin films formed using thermal annealing of predeposited layers of copper, zinc and tin sulphides on glass substrates at different temperatures and ambient atmosphere were determined. It has been shown that films grown at lower temperatures have the tetragonal structure of kesterite, and the corresponding value of the optical band gap is 1,47 eV.

The heat capacity Cp of solid Kr - n CH4 solutions with the CH4 concentrations n = 0,82, 0,86, 0,90 as well as solutions with n = 0,90, 0,95 doped with 0,002 O2 impurity has been investigated under equilibrium vapor pressure over the interval 1 - 24 K. The (T, n)-phase diagram was refined and the region of two-phase states was determined for Kr - n CH4 solid solutions. The contribution of the rotational subsystem, <$E C sub roman rot>, to the heat capacity of the solutions has been separated. Analysis of <$E C sub roman rot (T)> at <$E T~<<~3> K made it possible to estimate the effective conversion times <$E tau> and the energy gaps <$E E sub 1> and <$E E sub 2> between the tunnel levels of the A-, T- and A-, E-nuclear-spin species of CH4 molecules in the orientationally ordered subsystem, and to determine the effective energy gaps <$E E sub 1> between the lowest levels of the A- and T-species. The relations <$E tau (n)> and <$E E sub 1> (n)> stem from changes of the effective potential field caused as the replacement of CH4 molecules by Kr atoms at sites of the ordered sublattices. The effective gaps <$E E sub L> between a group of tunnel levels of the ground-state libration state and the nearest group of excited levels of the libration state of the ordered CH4 molecules in the solutions with n = 0,90 (<$E E sub L~=~52> K) and 0,95 (<$E E sub L~=~55> K) has been estimated.

The alloy of Ne - 5,1 % n-H2 was investigated calorimetrically under equilibrium vapor pressure in an interval of 0,9 - 25 K. The magnitudes and the temperatures dependencies of the heat capacity <$E C sub roman sol (T)> of the alloy at T = 11 - 20 K are strongly dependent on the conditions of sample preparation. The temperatures dependencies of the <$E C sub roman sol (T)> of the sample prepared in a calorimeter by direct condensation of a gas mixture at <$E T~symbol Ы~15> K exhibit a smeared maximum near the triple point temperature of hydrogen and a phase transition at T = 17,1 K. The detected features of <$E C sub roman sol (T)> indicate that the preparation of the solid Ne - n-H2 from a gas phase leads to the formation of a nonequilibrium long-living phase Ne with large H2 concentrations and a small portion of H2 inclusions with low Ne concentrations. The phase transition is caused by decompositions of this phase. The phase dose not recover on cooling the sample after the phase transition. It is found that the rate of the ortho-para conversion of the H2 molecules in the solid Ne - n-H2 solutions higher than that of solid H2.

Effect of pressure on electronic structure and magnetic properties of ferromagnetic <$E roman {GdM sub 2~(M~=~Mg,~Al,~Fe,~Co,~Ni,~Rh,~Ir,~ Pt)}> compounds and the reference <$E roman YCo sub 2> compound was studied experimentally and theoretically. Based on results of ab initio electronic structure calculations, the magnetic ordering temperatures and their pressure derivatives are estimated in the framework of the mean field models and appeared to be in improved agreement with experimental data. The origin of anomalous magnetovolume effect in <$E roman YCo sub 2> is revealed.

Застосовуючи симуляції з використанням методу молекулярної динаміки разом із атомним методом, що базується на методі LMT орбіталей із повним потенціалом, створено рівняння стану для гексагональної щільно упакованої (hcp або <$E epsilon>) фази заліза за високого тиску. Порівняння між існуючими експериментальними даними та обчисленнями наводить на думку, що одержане рівняння стану можна надійно використовувати для обчислення об'ємних властивостей заліза за умов, що відповідають кору Землі. Показано, що деякі експериментальні дані по залізу можуть піддаватися систематичній похибці. Запропоновано модель, яка описує температурну залежність об'єму краще, ніж рівняння Мі - Грюнайзена.

Theoretical and experimental data on melting at high pressure are often controversal. This is because of performing experiments at extreme conditions and difficulties with verification of theoretical models. In this paper, we look into details of mostly theoretical studies and compare different approaches to predict and/or describe melting pressure - temperature curves. Some experimental problems are also addressed. Recent results for melting of alkali halides, some oxides and metals (LiF, MgO, MgSiO₃, Cu, and Fe) obtained using molecular dynamic method and diamond anvil cell technique are analyzed.

Numerical simulation based on FPLAPW calculations is applied to study the lattice parameters, bulk modulus, band energy and optical properties of the zincblende binary AlN, GaN, InN under hydrostatic pressure. The results obtained are in a good agreement with experimental and theoretical values.

Експериментально досліджено із використанням методу світлорозсіювання утворення тріщин у монокристалах NaCl за умов одноосьового циклічного стискання (10<^>7 Н/м<^>2) протягом ~ 10 с за умови кімнатної температури та подальшого відпалу за T = 500 градусів за Цельсієм протягом 10 хв. Спостережувані тріщини за розмірами розділено (умовно, у порівнянні з довжиною хвилі світла, що використано) на малі, що надають ізотропну картину розсіювання, та великі, картина розсіювання світла якими містить різкі максимуми. Встановлено, що і малі, і великі тріщини розташовуються у площинах типу {100} і утворюються механізмом Коттрелла. На далеких стадіях деформування спостерігаються у невеликій кількості тріщини у площинах типу {110}. З можливих механізмів їх утворення у цьому випадку (малих деформацій і напружень) найбільш імовірним видається механізм Стро. Виявлено, у міру накопичення тріщин, утворення впорядкованих компактних груп тріщин, аналогічних упорядкованим групам твердих іншофазних виділень за розпаду пересичених твердих розчинів. Об'ємна частка малих тріщин на 2 порядки перевершує об'ємну частку великих. Об'ємні частки тих та інших зростають з номером циклу, але випереджальним темпом зростає частка великих тріщин.

The molecular phase of hydrogen converts to the atomic metallic phase at high pressures estimated usually as 300 - 500 GPa. We analyze the zero-temperature decay of metallic phase as the pressure is relieved below the transition one. The metallic state is expected to be in the metastable long-lived state down to about 10 - 20 GPa and decays instantly at the lower pressures. The pressure range of the long-lived metastable state is directly associated with an impossibility to produce a stable hydrogen molecule immersed into the electron liquid of high density. For lower pressures, the nucleation of an electron-free cavity with the energetically favorable hydrogen molecule inside cannot be suppressed with the low ambient pressure.

The wavelike processes of crystallization and melting or crystallization waves are well known to exist at the <^>4He crystal surface in the rough state. Much less is known about crystallization waves for the <^>4He crystal surface in the smooth well-faceted state below the roughening transition temperature. To meet the lack, we analyze here the spectrum of facet crystallization waves and its dependence upon the wavelength, perturbation amplitude, and the number of possible facet steps distributed somehow over the wavelength. All the distinctive features of facet crystallization waves from conventional waves at the rough surface result from a nonanalytic cusplike behavior in the angle dependence for the surface tension of smooth crystal facets.

Індекс рубрикатора НБУВ: В367 + В378.6 + К222.08

Рубрики:

Фізика високих та низьких тисків

Механічні властивості монокристалів металів

Вплив легувальних елементів і домішок на структуру і властивості залізних сплавів. Теорія легування. Леговані залізні сплави

Шифр НБУВ: Ж14388 Пошук видання у каталогах НБУВ 

Calculations of structural phase transitions В1 - В2 under pressure in chalcogenides of alkaline-earth metals were carried out on the basis of approach of the local density functional theory, where as a fitting used was the constructive amendments of the potential by means of the electronic density received in a self-coordinated calculation using the approximation of the local density.

The coefficients of interatomic potential of simple form Exp-6 for neon are obtained. Repulsive part is calculated ab-initio in the Hartree-Fock approximation using the basis of atomic orbitals orthogonalized exactly on different lattice sites. Attractive part is determined empirically using single fitting parameter. The potential obtained describes well the equation of state and elastic moduli of neon crystal in a wide range of interatomic distances and it is appropriate for molecular dynamic simulations of high-temperature properties and phenomena in crystals and liquids.

The T = 0 K equations of state (EOS) of rare-gas solids (RGS) (He, Ne, Ar, Kr, and Xe) are calculated in the experimentally studied ranges of pressures accounting for two- and three-body interatomic forces. Solid-state corrections to the pure two-body Aziz et al. potentials included the long-range Axilrod - Teller three-body interaction and short-range three-body exchange interaction. The energy-scale and length-scale parameters of the latter were taken as adjustable parameters of theory. The calculated T = 0 K EOS for all RGS are in excellent agreement with experiment in the whole range of pressures. The calculated EOS for Ar, Kr, and Xe exhibit inflection points where the isothermal bulk moduli have non-physical maxima indicating that account of only three-body forces becomes insufficient. These points lie at pressures 250, 200, and 175 GPa (volume compressions of approximately 4,8, 4,1, and 3,6) for Ar, Kr, and Xe, respectively. No such points were found in the calculated EOS of He and Ne. The relative magnitude of the three-body contribution to the ground-state energy with respect to the two-body one as a function of the volume compression was found to be non-monotonic in the sequence Ne - Ar - Kr - Xe. In a large range of compressions, Kr has the highest value of this ratio. This anomally high three-body exchange forces contributes to the EOS so large negative pressure that the EOS for Kr and Ar as a function of compression nearly coincide. At compressions higher approximately 3,5, the curves intersect and further on the EOS of Kr lies lower than that of Ar.

Теоретично вивчено природу зовнішніх і внутрішніх самозахопних носіїв струму в купратах. Енергії зв'язування та радіуси зовнішніх і внутрішніх великих поляронів і біполяронів в купратах обчислено варіаційно, використовуючи неперервну модель та адіабатичне наближення. Показано, що зовнішні та внутрішні тривимірні великі біполярони існують в слабозлегованих купратах, відповідно, за <$E eta~=~epsilon sub inf "/" epsilon sub 0~<<~0,127> і <$E eta~<<~0,138> [де <$E epsilon sub inf ( epsilon sub 0 )> - оптична (статична) діелектрична стала].

In the present paper we generalize a phenomenological model developed by Gomonay and Loktev (Fiz. Nizk. Temp. 31, 1002 (2005)) for the description of magnetostructural phase transitions and related peculiarities of elastic properties in solid oxygen under high pressure and/or temperature below 40 K. We show that variation of all the lattice parameters in the vicinity of <$E alpha~-~beta> phase transition is due to both the shift of basal closed-packed planes and appearance of the long-range magnetic order. Competition between these two factors from one side and lattice compression below <$E T sub {alpha beta}> from another produces nonmonotonic temperature dependence of lattice parameter b (along monoclinic axis). Steep decrease of the sound velocities in the vicinity of <$E T sub {alpha beta}> can be explained by the softening of the lattice with respect to shift of the close-packed planes (described by the constant <$E K sub 2>) prior to phase transition point. We anticipate an analogous softening of sound velocities in the vicinity of <$E alpha~-~beta> phase transition and nonmonotonic pressure dependence of sound velocities in <$E alpha> phase.

Here we review recent experimental and theoretical studies of hydrogen approaching metallization regime. Experimental techniques have made great advances over the last several years making it possible to reach previously unachievable conditions of pressure and temperature and to probe hydrogen at these conditions. Theoretical methods have also greatly improved; exemplified through the prediction of new structural and ordered quantum states. Recently, a new solid phase of hydrogen, phase IV, has been discovered in a high-pressure high-temperature domain. This phase is quite unusual structurally and chemically as it represents an intermediate state between common molecular and monatomic configurations. Moreover, it shows remarkable fluxional characteristics related to its quantum nature, which makes it unique among the solid phases, even of light elements. However, phase IV shows the presence of a band gap and exhibits distinct phonon and libron characteristic of classical solids. The quantum behavior of hydrogen in the limit of very high pressure remains an open question. Prospects of studying hydrogen at more extreme conditions by static and combined static-dynamic methods are also presented.

We report the results of Raman and synchrotron infrared absorption measurements of several molecular phases of solid nitrogen to pressures above 100 GPa (300 K). Low-temperature vibrational spectra to 45 GPa are also presented. The changes in Raman and infrared spectra at 60 GPa and 300 K are interpreted as arising from the <$E epsilon~symbol О~zeta > transition reported at low temperature. The character of splitting of the Raman vibron <$E nu sub 2 > observed at 25 GPa and low temperatures differs from that previously reported, a difference that we ascribe to different experimental procedures employed and metastability of the low-temperature phase.

Magnetic susceptibility <$E chi> of uranium compounds <$E roman U X sub 3~(X~=~roman {Al,~Ga,~Si,~Ge})> is studied under pressure up to 2 kbar in the temperature range 78 - 300 K. A pronounced pressure effect has been revealed, and the measured volume derivatives, <$E roman {d ln chi "/" d ln V}>, were found to be almost temperature-independent and equal to 2,3, 6,8, and 6,9 for <$E roman {USi sub 3 ,~UGa sub 3 }>, and <$E roman UGe sub 3>, respectively, at 78 K. In <$E roman UAl sub 3>, a noticeable temperature dependence of this derivative was obtained, ranging from <$E roman {d ln chi "/" d ln V}~=~11> at low temperatures to about 5,5 at Т = 300 К. The volume dependent electronic structures of the <$E roman U X sub 3> compounds have been calculated ab initio in the paramagnetic phase by employing a relativistic full-potential LMTO method. The calculations have brought out a predominance of itinerant uranium 5f states at the Fermi energy. The calculated field-induced magnetic moments in <$E roman U X sub 3> and their volume derivatives are in agreement with the experimental data on <$E chi>. An origin of the observed strong temperature dependence of the magnetovolume effect in <$E roman UAl sub 3> is also discussed.

Індекс рубрикатора НБУВ: В367 + В377.3

Рубрики:

Фізика високих та низьких тисків

Магнітні властивості твердих тіл. Магнетики

Шифр НБУВ: Ж14388 Пошук видання у каталогах НБУВ 
Повний текст  Наукова періодика України