Despite symmetrical polarization, the magnitude of a light-induced voltage is known to be asymmetric with respect to poling sign in many photovoltaic (PV) ferroelectrics (FEs). This asymmetry remains unclear and is often attributed to extrinsic effects. We show here for the first time that such an asymmetry can be intrinsic, steaming from the superposition of asymmetries of internal FE bias and electro-piezo-strictive deformation. This hypothesis is confirmed by the observed decrease of PV asymmetry for smaller FE bias. Moreover, the both PV effect and remanent polarization are found to increase under vacuum-induced expansion and to decrease for gas-induced compression, with tens percents tunability. The change in cations positions under pressure is analysed through the first-principle density functional theory calculations. The reported properties provide key insight for FE-based solar elements optimization.

Íà îñíîâ³ ñàìîóçãîäaeåíèõ ðîçðàõóíê³â ìåòîäîì ïñåâäîïîòåíö³àëó ïðîâåäåíî òåîðåòè÷íå âèâ÷åííÿ ñòðóêòóðíèõ ³ åëåêòðîííèõ âëàñòèâîñòåé ìîíîêðèñòàë³â InI ó øèðîêîìó ä³àïàçî-í³ çì³íè çîâí³øíüîãî òèñêó. ϳäòâåðäaeåíî âèçíà÷àëüíó ðîëü íàäëèøêîâî¿ 5s 2 åëåêòðîííî¿ ïàðè ³îíà In + ó ôîðìóâàíí³ ñòðóêòóðè òà ñòàá³ë³çàö³¿ ñïîëóê, ùî ì³ñòÿòü êàò³îíè ³ç çíèaeåíîþ âàëåíòí³ñòþ. Âèçíà÷åíî çíà÷åííÿ ãðàíè÷íîãî òèñêó ôàçîâîãî ïåðåõîäó InI ó âèñîêîñèìåò-ðè÷íèé ñòðóêòóðíèé òèï CsCl. Âñòàíîâëåíî, ùî ïåðåä ñòðóêòóðíèì ïåðåõîäîì â³äáóâàºòüñÿ ïåðåõ³ä íàï³âïðîâ³äíèê-ìåòàë. ϳñëÿ ñòðóêòóðíîãî ïåðåõîäó ñïîëóêà çàëèøàºòüñÿ íàäàë³ êâàç³îäíîì³ðíèì ìåòàëîì.

Using density functional theory calculations, we studied structural, electronic and adsorption properties of CO and H 2 adsorption on the Pt-doped (ZnO) 12 nanoclusters. The more suitable position for the Pt atom is its lateral doping on the nanocluster surface. The lower energy gap for the Pt-doped (ZnO) 12 nanoclusters denotes that their conductivity is higher in comparison with the bare nanocluster. The results showed quite a reasonable increase in CO and H 2 gas molecules adsorption energies on the nanoclusters compared with the pristine (ZnO) 12 due to Pt doping. The sensitivity of the electronic and adsorption properties to the number of molecules was calculated as well. Upon CO adsorption on the Pt-doped (ZnO) 12 nanoclusters energy, it is better when no more than two molecules can be attached to one Pt atom, while H 2 adsorption provides at least three hydrogen molecules on Pt atom. Also, changes in electronic spectra of nanoclusters under the influence of adsorbed CO and H 2 molecules imply a decline in conductivity in such systems. These investigations proved that the Pt-doped (ZnO) 12 nanoclusters can be proposed as an approachable candidate in gas sensors for detecting CO and H 2 gas. Also, the calculation results of H 2 adsorption on Pt-doped (ZnO) 12 nanoclusters can help in consideration of the possibility of hydrogen storage media creation.

A series of InxTl1−xI (x = 0.4−0.9) single crystalline solid state alloys were successfully synthesized by the vertical Bridgman method. For the first time the density functional theory based band structure calculations are performed and features of the band energy dispersion are discussed. Comparison with the experimental energy gap Eg obtained from the optical photoconductivity is discussed. An essential role of the localized defects and excitons in formation of the edge photoconductivity is analyzed. Relation between the crystal structure and photoconductivity of the materials studied is discussed. Also the origin of the principal valence and conduction bands is explored. Experimental measurements of the band gap Eg by the optical and photoconductivity methods have given opposite dependences with respect to the indium content x. Features of the photoconductivity spectra for different crystallographic directions have been discussed with taking into account the chemical bonds anisotropy.

Density functional theory studies of the structural and electronic properties of nanoclusters (ZnO)n (n = 34, 60) in different geometric configurations were conducted. For each cluster, an optimization (relaxation) of structure geometry was performed, and the basic properties of the band structure were investigated. It was established that for the (ZnO)34 nanoclusters, the most stable are fullerene-like hollow structures that satisfy the rule of six isolated quadrangles. For the (ZnO)60 nanoclusters, different types of isomers, including hollow structures and sodalite-like structures composed from (ZnO)12 nanoclusters, were investigated. It was determined that the most energetically favorable structure was sodalite-type structure composed of seven (ZnO)12 clusters with common quadrangle edges.