Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H
O molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at ...a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective. Here, we present measurements of the temperature-dependent dielectric permittivity, pyrocurrent, electric polarization and specific heat that indicate an order-disorder ferroelectric phase transition at T
≈ 3 K in the water dipolar lattice. Ab initio molecular dynamics and classical Monte Carlo simulations reveal that at low temperatures the water molecules form ferroelectric domains in the ab-plane that order antiferroelectrically along the channel direction. This way we achieve the long-standing goal of arranging water molecules in polar order. This is not only of high relevance in various natural systems but might open an avenue towards future applications in biocompatible nanoelectronics.
DebyeFit is a simple tool to calculate the Debye or Einstein characteristic temperature of thermal vibrations in crystals from the equivalent atomic displacement parameters (ADPs) of any atom ...obtained at several temperatures. The ADP values are separated into static and dynamic components to get a best fit to the Debye, Einstein or mixed model. The static term is added to account for possible static disorder. A nonlinear least‐squares technique is used to refine the parameters of the model for sets of ADPs observed in multi‐temperature structural studies. The program provides a good fit between theoretical and observed ADP values.
DebyeFit is a computer program that calculates the Debye/Einstein characteristic temperature of atomic vibrations in solids using equivalent atomic displacement parameters (ADPs) determined at several temperatures. An optimal fit is achieved if ADPs are modeled with both static and dynamic components.
The atomic structure of a single crystal of Sr
0.75
Ba
0.25
Nb
6
O
2
representing a relaxor ferroelectric is determined from X-ray diffraction data. At nine temperatures within a range of 93–480 K, ...12 experiments are performed. The experimental facilities (area detector, goniometer, and sample cooling system) are calibrated. The region of negative thermal expansion with respect to the unit-cell parameter
с
is revealed at 272–324 K. In the same region, an electrical resistance anomaly is observed. It is found that the structural parameters have a singularity at 296 K, in particular, an unusual thermal motion of atoms is observed. This correlates with a kink in the resistance–temperature curve at 297.5 K. The obtained results and analysis of published data indicate that, near room temperature, several physical properties of Sr
0.75
Ba
0.25
Nb
6
O
2
relaxor at once have singularities, which can be explained by the revealed lattice instability.
A new approach to the structural analysis of crystals based on diffraction data obtained in a series of experiments performed at different temperatures (i.e., to the multitemperature structural ...characterization) is proposed and implemented. Calculations are performed using symmetry-averaged diffraction data. The full-matrix least-squares method is applied to calculate simultaneously the composite structural model from several datasets. The main purpose of the proposed algorithm is to determine which of the refined parameters are general (temperature-stable) and which reflect the dataset individuality (i.e., change with temperature). The method is applied to determine the occupancies of mixed atomic sites in rubidium titanyl phosphate doped with zirconium, to search for the mobile atoms responsible for the ion transport in this crystal, and to study the structural evolution of the boron framework in crystals of rare-earth element dodecaborides (
R
B
12
) of several compositions.
Unique methods for processing diffraction data, which guarantee extreme accuracy and reliability, have been implemented in the ASTRA 4.0 software package. The central (data-forming) element is a ...program for averaging intensities of repeated and equivalent reflections. The ASTRA averaging algorithm makes it possible to calculate the average intensity and its standard uncertainty, which correspond to normal distribution law for errors in data. Such data yield an unbiased estimate of the parameters of refined structural model at minimum reliability factors. To make the averaging program successfully operate, one must introduce all corrections for anisotropic effects into the reflection’s intensities. The following stages of investigation are considered: sample preparation; calibration of diffractometer; and correction for absorption, thermal diffuse scattering, and simultaneous reflections. A significant advantage of the proposed approaches is proven on several examples.
Accurate X-ray diffraction study of langasite (La
3
Ga
5
SiO
14
) single crystal has been performed using the data obtained on a diffractometer equipped with a CCD area detector at 295 and 90.5 K. ...Within the known La
3
Ga
5
SiO
14
model, Ga and Si cations jointly occupy the 2
d
site. A new model of a “multicell” consisting of two different unit cells is proposed. Gallium atoms occupy the 2
d
site in one of these cells, and silicon atoms occupy this site in the other cell; all other atoms correspondingly coordinate these cations. This structure implements various physical properties exhibited by langasite family crystals. The conclusions are based on processing four data sets obtained with a high resolution (sin θ/λ ≤ 1.35 Å
–1
), the results reproduced in repeated experiments, and the high relative precision of the study (sp. gr. P321,
Z
= 1; at 295 K,
a
= 8.1652(6) Å,
c
= 5.0958(5) Å,
R/wR
= 0.68/0.68%, 3927 independent reflections; at 90.5 K,
a
= 8.1559(4) Å,
c
= 5.0913(6) Å,
R/wR
= 0.92/0.93%, 3928 reflections).
The multicell model alternative to the model of mixed atomic sites used now is proposed for a single crystal of La
3
Ga
5
GeO
14
belonging to the langasite family. The multicell consists of four unit ...cells. In three identical cells of the structure, atoms adapt to the Ge atom occupying one of the two 2
d
positions on the threefold symmetry axis. In the fourth cell, atoms surround the Ge atom located at the 1a position. The multicell model allows one to study the short-range order of atoms by the methods of classical structure analysis based on Bragg scattering. Four high-resolution data sets measured at 295 and 111.5 K are used in the study. The results are obtained with high relative precision (space group
P
321,
Z
= 1; at 295 K
a
= 8.2020(6) Å and
c
= 5.1065(6) Å,
R/wR
= 0.81/0.73% for 3829 unique ref lections; at 111.5 K a = 8.1939(1) Å and c = 5.1022(4) Å,
R/wR
= 0.85/0.76% for 3880 reflections).
An accurate structure analysis of a Ba
3
TaGa
3
Si
2
O
14
single crystal from langasite family was performed using four X-ray diffraction data sets collected on a diffractometer equipped with a CCD ...area detector (sp. gr.
P
321,
Z
= 1, sinθ/λ ≤ 1.35 Å
–1
; at 295 K
a
= 8.516(1) Å,
c
= 5.1910(6) Å,
R
/
wR
= 0.58/0.56%, Δρ
min
/Δρ
max
=–0.73/0.42 e/Å
3
, 4414 independent reflections; at 106 K
a
= 8.5109(9) Å,
c
= 5.1861(9) Å,
R
/
wR
= 0.75/0.86%, Δρ
min
/Δρ
max
=–0.81/1.06 e/Å
3
, 4382 reflections). The distinguishing feature of the Ba
3
TaGa
3
Si
2
O
14
structure is a strong disorder of the Ga atom at the 3
f
site. Structural transformations in the series of Сa
3
TaGa
3
Si
2
O
14
–Sr
3
TaGa
3
Si
2
O
14
–Ba
3
TaGa
3
Si
2
O
14
–Ba
3
TaFe
3
Si
2
O
14
crystals were analyzed.
Fibroblast growth factor receptors (FGFR) are cell surface tyrosine kinases that function in cell proliferation and differentiation. Aberrant FGFR signaling occurs in diverse cancers due to gene ...amplification, but the associated oncogenic mechanisms are poorly understood. Using a proteomics approach, we identified signal transducers and activators of transcription-3 (STAT3) as a receptor-binding partner that is mediated by Tyr(677) phosphorylation on FGFR. Binding to activated FGFR was essential for subsequent tyrosine phosphorylation and nuclear translocation of STAT3, along with activation of its downstream target genes. Tyrosine phosphorylation of STAT3 was also dependent on concomitant FGFR-dependent activity of SRC and JAK kinases. Lastly, tyrosine (but not serine) phosphorylation of STAT3 required amplified FGFR protein expression, generated either by enforced overexpression or as associated with gene amplification in cancer cells. Our findings show that amplified FGFR expression engages the STAT3 pathway, and they suggest therapeutic strategies to attack FGFR-overexpressing cancers.
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