Дослідження оптичного поглинання та п’єзоелектричного ефекту у монокристалі твердого розчину AgGaGe3Se7.6Te0.4

In present work spectral distribution of absorption coefficient in the range of 100 – 300 K was investigated and band gap values  evaluated. Parameters of Urbach rule were calculated and linearity  of temperature dependence of Urbach energy was showed. Thermo induced piezoelectric effect in a range of 297 ‑ 357 K was investigated. Laser induced kinetics of piezomodule was investigated and absence of irreversible changes was showed. Influence of heating the crystal during laser illuminating on piezoelectric module was adjusted.У даній роботі досліджено спектральний розподіл коефіцієнта поглинання в діапазоні температур 100 – 300 К, оцінена ширина забороненої зони. Показана експоненційна залежність коефіцієнта поглинання в області краю поглинання, розраховані параметри правила Урбаха. Досліджено температурно- та лазерно- індукований п’єзоелектричний ефект. Скорегован

Band Structure Calculation and Optical Properties of Ag3AsS3 Crystals

In the study, band structure calculation in the points of high symmetry of the first Brillouin zone and alongside the lines that connect them has been derived by using CASTEP programs in which the pseudopotential method with the basis in the form of plane-waves is realized. The calculated value of the lattice parameters using GGA functional is well correlated with experimental data. According to the band diagram that was built for the Ag3AsS3 crystal using GGA method, band gap has an indirect type. The calculated value of the band gap is  = 1.22 еV. The experimental value of the band gap obtained by Tauc’s method is  = 2.01 еV,  = 2.17 еV. Full and partial density of N(E) states for contributions of separate atoms has been calculated. As a result, the top of the valence band is formed by 3p-states of S atoms and the bottom of the conduction band is formed by 5s-states of Ag atoms and 3p-states of S atoms

ІЧ-фотоіндуковані п'єзоелектричні ефекти у багатокомпонентних халькогенідах Ag2In(Ga)2Si(Ge)S(Se)6

The influence of external irradiation of CO2, CO, Er:glass, Nd:YA lasers on the piezoelectric properties of the Ag2In(Ga)2Si(Ge)S(Se)6 crystals was investigated. The maximum photoinduced changes in the piezoelectric coefficient were observed after irradiation with CO2 laser. CO photoinducing bicolour beams with 5.5 μm wavelength cause at least 4 times smaller increase in piezoelectric coefficients. Therefore, it can be expected that the primary mechanisms cause the excitation of the phonon subsystem.Досліджено вплив зовнішнього опромінення лазерів CO2, CO, Er: скла, Nd: YA на п'єзоелектричні властивості кристалів Ag2In(Ga)2Si(Ge)S(Se)6. Максимальні фотоіндуковані зміни п'єзоелектричного коефіцієнта спостерігалися після опромінення CO2 лазером. Фотоіндукційні двоколірні промені з довжиною хвилі 5,5 мкм викликають принаймні в 4 рази менший приріст п’єзоелектричних коефіцієнтів. Тому можна очікувати, що первинні механізми викликають збудження фононної підсистеми

Influence the cationic substitution in AgGaGe₃Se₈ on the electro-optical, IR optical and nonlinear properties

In present article we present results of detailed study of the possibility adapting AgGaGe3Se8 single crystal properties to desired requirements by investigate the influence of the different cationic substitution on the physical properties: optical, nonlinear optical (NLO) - Second Harmonic Generation (SHG) and temperature dependent photoconductivity. We report results obtained for modified crystals based on AgGaGe₃Se₈ by cationic substitution of the elements belong to first - (Ag-Cu), third (Ga-In), and fourth (Ge-Sn) groups of the periodic system. For the convincing observation the effects of various impurities and compare results with obtained for virgin AgGaGe₃Se₈ crystal was conducted replacing at 5 mol. % one element by another

Склосистема Tl2S – In2S3 – GeS2 як новітні перспективні матеріали для фотоніки

It was established that minimal content of the glass-forming component GeS2 is equal to 30 mol.% (by exploration the set of 23 different alloys with different composition). Correlation between structural properties, thermal parameters (glass transition, crystallization and melting temperatures) and optical absorption spectra along of the titled glasses system has been found. The temperatures, the band gap energy and the characteristic energy of vitreous alloys for the gastric system Tl2S‑In2S3‑GeS2 were investigated experimentally.Встановлено, що мінімальний вміст складоутворюючого компонента GeS2 дорівнює 30 мол.% (досліджували набір 23 різних сплавів з різним складом). Встановлено взаємозв'язок між структурними властивостями, термічними параметрами (температура склa, температури кристалізації та плавлення) та оптичними спектрами поглинання. Експериментально досліджені температури, енергія розриву смуг та характерна енергія склоподібних сплавів для системи Tl2S‑In2S3‑GeS2

Особливості фотопровідність монокристалів Tl1-xIn1-xSnxSe2 при низьких температурах

The photoconductivity spectra in the temperature range T≈36-200 K and the spectra of thermostimulated currents in the temperature range T≈70-300 K of Tl1-xIn1-xSnxSe2 single crystals obtained by directional crystallization of Bridgman-Stockbarger have been studied. The induced photoconductivity and long-term photoconductivity relaxation processes have been found. To interpret the found results, a model of two-center recombination has been suggested. It is illustrated that the role of the r-centers of slow recombination are formed by Tl vacancies. On the basis of the studies of the spectra of thermally stimulated currents, the thermal energy of electrons activation with t-levels of adhesion has been determined.Основні результати досліджень полягають у тому, що особливістю низькотемпературної фотопровідності монокристалів Tl1-xIn1-xSnxSe2 є домішкова та індукавана фотопровідність, а також довготривалі процеси релаксації фотопровідності. Оцінене значення часу релаксації фотопровідності становило ~102-103 с. Термічна енергія активації електронів з t-рівнів у монокристалах Tl0,75In0,75Sn0,25Se2 становила 0,13 еВ та 0,28 еВ. Зменшення вмісту Sn в Tl1-xIn1-xSnxSe2 призводить до зменшення глибини залягання цих рівнів. У монокристалах Tl0,9In0,9Sn0,1Se2існує три дефектні центри, які виконують роль t-рівнів прилипання у різних температурних інтервалах

Transport Phenomena In Single Crystals Tl1−XIn1−XGeXSe2 (x=0.1, 0.2)

Temperature dependences of electroconductivity for single crystals Tl1−xIn1−xGexSe2 were analyzed. It was established an occurrence of thermoactivated states within the temperature range 100-300 K. The conductivity is formed by delocalized carriers within the conductivity band and the jumping conductivity over the localized states which are situated in the narrow localized states near the Fermi level. Following the performed data the activation energy was evaluated with accuracy up to 0.02 eV. The density of the localized states as well as the distribution of the energy over the mentioned states was evaluated. Additionally the average distance between the localized states is evaluated at different temperatures

Optical features of novel semiconducting crystals Tl1–xGa1–xSnxSe2 (x=0.05; 0.1)

The results of the novel Tl1–xGa1–xSnxSe2 single crystals (x = 0.05; 0.1) growth together with complex studies of their optical, electric and photoelectric properties are presented. Semiconductor crystalline alloys Tl2Sе, Ga(In)2Sе3, SnSе2 possessing congruent melting features has been served as components for the quasi-ternary systems. The Tl2Se–Ga2Se3 was melted congruently at temperature 1073 K. Two compounds existied for the Tl2Sе–In2Sе3system: TlInSe2 melting congruently at 1023 K, and Tl2Sе–In2Sе3 within congruent melting nature at 1029 K. Isothermal section of the Tl2Se–Ga2Se3–SnSe2 system at 520 K have been constructed from X-ray phase and formation of the ternary compounds Tl4SnSе4, Tl2SnSе3, TlGaSе2 was confirmed. The spectral dependences of the absorption coefficients near the fundamental absorption have been studied with respect to direct as indirect dipole allowed inter-band transitions realized in the (TlGaSe2)1-x(SnSe2)x crystals for the studied temperature range. Follwing the Urbach's energy the role of electron-phonon interaction and structural disorder was analyzed. © 2019 Elsevier Gmb