The effect of rapid thermal annealing (RTA) at 950 and 1000 °C for 3 min on the photoluminescence (PL) in multilayered (~50 layers) nanoperiodical (4/3 nm) a-SiOx/SiO2 and a-SiOx/ZrO2 nanostrucutres (MNS) synthesized using vacuum evaporation has been analyzed in comparison with conventional long-term (~1 h) high-temperature annealing (HTA). It has been shown that the use of sequential anneals (RTA + HTA) at 1000 and 1100 °C, respectively, allows increasing the intensity of the PL band of silicon nanocrystals (at ~800 nm) by 2.5 times as compared with conventional heat treatment. Analysis of the PL spectra suggests that RTA triggers the formation of chain and ring non-phase silicon inclusions and/or small-sized Si nanocrystals (~2 nm) which generate radiation near 600 nm at room temperature. Thus, one can conclude that RTA produces elevated concentrations of the abovementioned silicon nuclei which, upon subsequent HTA, serve as growth centers for larger Si nanocrystals (~3–4 nm). It has been found that SiOx/ZrO2 MNS exhibit a similar behavior (qualitative) of PL spectra after RTA. However, the PL intensity in this case is 5–10 times lower, due to the chemical interactions between the materials of the MNS layers with the formation of zirconium silicides and silicates.
The paper studies the effect of nickel ferrite addition and sintering temperature on the density, dielectric and piezoelectric characteristics of barium titanate ceramics. A density jump is detected, when with an increase in the ferrite content the density first increases and then drops sharply. Moreover, if at a sintering temperature of 1200 °C the maximum density (5.38 g/cm3) occurs at a ferrite concentration of 0.05 mol.%, then at a sintering temperature of 1300 °C the maximum density (5.62 g/cm3) shifts to the region of higher ferrite concentrations and is 0.1 mol.%. Thus, it can be stated that at a sintering temperature of 1300 °C the ferrite addition in an amount of 0.1 mol.% acts as a sintering activator. X-ray phase analysis showed that in alloyed barium titanate the tetragonal splitting of lines is expressed more strongly, and the calculated lattice parameters a and c differ significantly from the parameters of pure barium titanate. The addition of 0.1 mol.% ferrite lowers the Curie temperature of the phase transition from the cubic phase to the tetragonal phase from 117 to 108.5 °C. Activation of the sintering process with the addition of ferrite up to ~0.1 mol.% makes it possible to reduce the sintering temperature to 1300 °C and obtain ceramics with high functional characteristics. Relative density is 93%, specific resistance is ~1010 Ohm·m, permittivity is 1500, piezoelectric modulus d31 is 85 pC/N, electromechanical coupling coefficient is 0.37.
Phase transformations during crystallization of the magnetic metal-oxide compound Sr2Fe1.2Mo0.8O6-δ by the solid-phase reactions method from a mixture of simple reagents 2SrCO3 + 0.6Fe2O3 + 0.8MoO3 have been analyzed. By means of differential-thermal and thermogravimetric analyses it was found that the synthesis of strontium ferromolybdate of the Sr2Fe1.2Mo0.8O6-δ composition proceeds through a series of successive-parallel stages. In this way, when considering the dynamics of phase transformations, it has been found that the main accompanying compounds during the crystallization of the solid solution of double perovskite Sr2Fe1.2Mo0.8O6-δ are Fe2O3, SrCO3, SrMoO4 and SrFeO3. When analyzing the phase composition of the batch consisting of a mixture of initial reagents of stoichiometric composition: 2SrCO3 + 0.6Fe2O3 + 0.8MoO3, it was noted that with an increase in temperature, complex compounds SrMoO4, SrFeO3, and then Sr2Fe1.2Mo0.8O6-δ as well, appear almost simultaneously. This circumstance indicates that the compounds SrMoO4 and SrFeO3 are the structure-forming ones for the solid solution of ferromolybdate – strontium. With a subsequent increase in temperature to 1470 K, it was found that the dissolution of SrFeO3 with the formation of double perovskite Sr2Fe1.2Mo0.8O6-δ occurs faster than the dissolution of strontium molybdate SrMoO4. The results of the analysis indicate the difficult nature of the dynamics of solid-phase reactions during the formation of Sr2Fe1.2Mo0.8O6-δ.
Nanostructured copper oxides (CuO, Cu2O) are regarded as promising anode materials for lithium-ion batteries (LIBs) due to owing high theoretical specific capacity and efficient conversion reaction mechanism with lithium under moderate conditions. On investigating the cyclic characteristics of binder-free CuO/Cu2O anodes at 1C current rate, first charge and discharge capacities were observed to be 455.4 and 431.9 mAh/g, respectively, with a Coulombic efficiency of 94.8 %. However, a gradual mitigated capacity was evident as the discharge capacity was decreased to 352.2 mAh/g by the 20th cycle, which can be attributed to solid electrolyte interphase (SEI) layer formation, electrode degradation, or loss of lithium. Beyond 20th cycles, the battery exhibited a more stable cycling regime, with Coulombic efficiency stabilizing ranging around 82–85 %. By the 40th cycle, discharge capacity was further declined to 339 mAh/g, indicating the ongoing degradation mechanisms, however at a much lower rate, such as SEI layer thickening and electrode pulverization. However, despite the initial instability, the system demonstrated enhanced consistency in later cycles, emphasizing the potential of nanostructured copper oxides as efficient LIB anodes. Future efforts should focus on mitigating long-term capacity fading to enhance performance and cycle life.
This paper analyzes properties of the dielectric/AlGaN/GaN system with an ALD Al2O3 film as a dielectric. It was investigated how the current flow process in the system changes due to the deposition of films with different thicknesses; at what bias voltage the electron emission process from the boundary states begins, and how the properties of the barrier layer in the initial heterostructure affect the parameters of the current in the system. It was found that a positive charge forms at the Al2O3/AlGaN interface, the charge magnitude increasing with the film thickness. It was also shown that film deposition affects the charge magnitude in the channel. It was demonstrated that the frequency at which C–V measurements are carried out affects Dit, i.e., the distribution of the electron states at the boundaries of the Al2O3/AlGaN/GaN system. It was shown that the density of the detected donor-like states increases abruptly with an increase in the measurement frequency. It was furthermore demonstrated that a correctly chosen measurement scheme allows one to estimate the potential contribution of the two boundaries, i.e., AlGaN/GaN and Al2О3/AlGaN, in this case, some of the electrons may remain in the channel.
