Polycrystals of the BiFe
2
(PO
4
)
3
compound and Bi
1 –
x
Sb
х
Cr
2
(PO
4
)
3
solid solution, which form a family isostructural to α-CaMg
2
(SO
4
)
3
(sp. gr.
P
6
3
/
m
), have been synthesized ...from an aqueous solution by the salt co-precipitation method. The samples are characterized by X-ray diffraction, IR spectroscopy, differential thermal analysis, and thermogravimetry, microprobe analysis. The BiFe
2
(PO
4
)
3
single crystals have been grown by the flux method. The structure consists of polyhedra of three types: PO
4
tetrahedra, two face-sharing FeO
6
octahedra, and BiO
6
octahedra. Isolated PO
4
tetrahedra, which share oxygen vertices with doubled FeO
6
octahedra, form a three-dimensional Fe
2
(PO
4
)
3
3∞
framework, whose voids are occupied by bismuth atoms. Structures of the BiFe
2
(PO
4
)
3
and NASICON types are compared.
A photodetector heterostructure based on AlInSb/InSb was grown by molecular-beam epitaxy. Mesostructures of different diameters were fabricated. The temperature dependence of the dark current was ...measured. It was demonstrated that the built-in barrier blocks the flow of majority charge carriers, thus reducing the dark-current density (relative to that for a
pin
structure based on InSb). The measured dependence of the dark current on the mesostructure size revealed that the bulk current component prevails over the surface one.
•Glass samples of GeSx90I10 (x=1.5, 1.7, 2.0, 2.3, 2.45, 2.6) compositions were prepared.•Optical, thermal properties and crystallization ability of GeSx90I10 glasses were investigated.•For the first ...time, Ge–S–I glass fibers were produced.
Glass samples of GeSx90I10 (x=1.5, 1.7, 2.0, 2.3, 2.45, 2.6) compositions were prepared, and some their thermal, optical properties as well as tendency to crystallization were investigated. The compositional dependences of glass transition temperature, volume fraction of crystallized phase and activation energy of glass formation (Eg) have nonmonotonic character with a maximum for GeS2.090I10 glass. Glasses of 85.8GeS2–14.2GeI4 and GeS1.590I10 compositions are identified as promising for preparation of optical fiber. For the first time, Ge–S–I glass fibers were produced. Minimum optical losses in 85.8GeS2–14.2GeI4 glass fiber were 2.7dB/m at a wavelength of 5.1μm, and that in GeS1.590I10 glass fiber were 14.5dB/m at 5.5μm.
GeSI2 and Ge2S3I2 glasses are prepared by interaction of germanium(IV) iodide, germanium and sulfur in evacuated silica-glass ampoules at temperatures of 450°C and 550°C, respectively. Germanium(IV) ...sulfide and germanium(IV) iodide are determined by means of X-ray diffraction analysis and energy-dispersive X-ray microanalysis as the main products of their decomposition. The kinetics of decomposition of these glasses under polythermal conditions is investigated in the temperature range of 50–850°C by means of thermogravimetric analysis and differential scanning calorimetry. The values of the activation energy of alloy decomposition, corresponding to the most intense period of acceleration, are 72.8±1.0kJ/mol for GeSI2 and 192±29kJ/mol for Ge2S3I2.
•The GeSI2 and Ge2S3I2 glasses were prepared from GeI4, Ge and sulfur.•The products of thermal decomposition of GeSI2 and Ge2S3I2 were determined.•The kinetics of decomposition of these glasses was investigated.
The synthetic mineral urusovite CuAl (AsO sub(4))O was prepared through the wet chemistry route and characterized over a wide temperature range in terms of studies of magnetization, specific heat, ...and X-band electron spin resonance. The basic structural units of the compound are distorted square pyramids CuO sub(5) assembled into corrugated honeycomb layers separated by AsO sub(4) and AlO sub(4) tetrahedrons. Both thermodynamic and resonant measurements indicate that CuAl (AsO sub(4))O is a spin gap system with a gap of ~ 350 K. The electronic structure calculations performed within the framework of density functional theory suggest a weakly interacting dimer model with antiferromagnetic signs for both intradimer and interdimer superexchange interactions. This establishes the valence bond solid as the quantum ground state of the title compound. The pronounced discrepancy between experimental data and calculations within the weakly interacting dimer model at elevated temperatures is ascribed in part to the steep increase of the intradimer exchange interaction parameter driven by the thermal expansion effects.
Characteristics of the sensing element of a fiber sensor for evanescent wave mid-IR spectroscopy have been studied within the electromagnetic theory of fiber waveguides by using the problem of ...determining the concentration of aqueous acetone solutions as an example. A multimode chalcogenide fiber was used as a sensing element. It has been shown that the selective excitation of the fiber modes may provide the possibility to increase the sensitivity of the fiber sensing element, decrease the minimum detectable concentration of a substance in a solution, and enhance the range of measured solution concentrations.
Glass samples of the Ge–Sb–Se–I system were prepared by reacting germanium tetraiodide and antimony triiodide with selenium in a set-up which provides selective removal of iodine from the melt. ...Thermodynamic modeling of purification reactions of the components is shown. The glasses are analyzed by X-ray spectral microanalysis, differential scanning calorimetry, IR spectroscopy, Raman scattering spectroscopy, and laser mass spectrometry. In the purest examples of these glasses, the content of residual impurities is: hydrogen—0.1ppmmol, silicon—0.02ppmwt., and transition metals—less than 0.5ppmwt.
•A new method for preparation of Ge–Sb–Se–I glasses has been developed.•Thermodynamic modeling of heterogeneous equilibrium in GeI4–Se system was performed.•The produced Ge–Sb–Se–I glasses are characterized by low content of impurities.
Introduction
. Cognitive impairments are important components of the clinical picture of many neuropsychiatric disorders, and are in dire need of evidence-based pharmacotherapeutic approaches.
The ...objective
was to test a model of delayed cognitive impairments due to neonatal administration of NMDA receptor antagonists (7th, 9 th, and 11 th days of life).
Methods and materials
. Male Wistar rats were administered with phencyclidine, 10 mg/kg (Experiment 1), or (+)MK-801, 1 mg/kg (Experiment 2); then «2-choice serial reaction time task», or «reinforcement learning task based on response patterning under interval schedules of reinforcement» in the same adult rats were performed.
Results
. Experiment 1: rats after neonatal NMDA-blockade performed operant tasks more accurately and made fewer missed attempts as compared to control. Experiment 2: switching to another schedule of reinforcement increased the pause after reinforced responses in both groups; in the experimental group, the duration of the post-reinforcement pause was shorter.
Conclusion
. Neonatal NMDA receptor blockade affects inhibitory control and attention to sensory stimuli, which manifests, respectively, as increased impulsivity and hyperfocusing in limited-choice conditions.
The concentration of hydroxyl groups in different types of quartz glass tubes, the OH concentration profile across the tube wall, and the kinetics of OH removal during heat treatment in the ...temperature range 750–950°C have been studied by Fourier transform IR spectroscopy. For TK-I tubes, produced by vacuum electromelting of quartz, followed by annealing in a hydrogen atmosphere, we have calculated the diffusion coefficient of OH groups in this temperature range and the activation energy for diffusion: 215 ± 10 kJ/mol. We have found heat treatment conditions that ensure a considerable decrease in the concentration of OH groups in quartz tubes that are used in the fabrication of reactors for the preparation of extrapure chalcogenide glasses.
The LiZr
2
(AsO
4
)
3
arsenate and LiZr
2
(AsO
4
)
x
(PO
4
)
3 −
x
solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray ...structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤
x
≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr
2
(AsO
4
)
3
(sp. gr.
P
2
1
/
n
,
a
= 9.1064(2),
b
= 9.1906(2),
c
= 12.7269(3) Å, β = 90.844(2)°,
V
=1065.03(5) Å
3
,
Z
= 4; sp. gr.
R
c
,
a
= 9.1600(4),
c
= 22.9059(13) Å,
V
= 1664.44(14) Å,
Z
= 6) and LiZr
2
(AsO
4
)
1.5
(PO
4
)
1.5
. Their structural frameworks are built up of AsO
4
tetrahedra—or (As,P)O
4
tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO
6
octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr
2
(AsO
4
)
x
(PO
4
)
3 −
x
with 0 ≤
x
≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.
