333 research outputs found
Effects of atomic short-range order on the properties of perovskite alloys in their morphotropic phase boundary
The effects of atomic short-range order on the properties of
Pb(Zr_{1-x}Ti_x)O_3 alloy in its morphotropic phase boundary (MPB) are
predicted by combining first-principles-based methods and annealing techniques.
Clustering is found to lead to a compositional expansion of this boundary,
while the association of unlike atoms yields a contraction of this region.
Atomic short-range order can thus drastically affect properties of perovskite
alloys in their MPB, by inducing phase transitions. Microscopic mechanisms
responsible for these effects are revealed and discussed.Comment: 4 pages, with 2 postscript figures embedded. Uses REVTEX4 and
graphicx macro
Equilibrium Moisture Content Importance in Safe Maritime Transport of Black Tea
In sea transport, a very important thing is an assignment of cargo to a particular class of storage climate conditions and it is carried out on the basis of the requirements that cargo places upon its storage atmosphere. The water content of black tea must not fall below 2%, as the product otherwise becomes hay-like and its essential oils readily volatilize, while on the other hand, it must not exceed 9% as it then has a tendency to grow mould and become musty. Therefore, tea requires particular temperature, humidity/moisture and possibly ventilation conditions. In this context, tea is a hygroscopic material that has the ability to absorb or desorb water in response to temperature and relative humidity of the atmosphere surrounding it. The moisture content of tea is one of the most important variables affecting its chemical and sensory properties. Therefore, to explore and predict the behaviour during transport of tea, its equilibrium moisture content must be determined for a range of transport temperatures and relative humidities. The present paper focuses on the evaluate the hygroscopic properties of tea from Rwanda with different degree of fragmentation based on isotherms of water vapour sorption and characteristics selected parameters of the surface microstructure determining transport conditions and therefor microbiological stability of teas
Structure and dielectric response in the high ferroelectric Bi(Zn,Ti)O-PbTiO solid solutions
Theoretical {\em ab initio} and experimental methods were used to investigate
the Bi(Zn,Ti)O-(1-)PbTiO (BZT-PT) solid solution. We find that
hybridization between Zn 4 and O 2 orbitals allows the formation of
short, covalent Zn-O bonds, enabling favorable coupling between A-site and
B-site displacements. This leads to large polarization, strong tetragonality
and an elevated ferroelectric to paraelectric phase transition temperature.
nhomogeneities in local structure near the 90 domain boundaries can be
deduced from the asymetric peak broadening in the neutron and x-ray diffraction
spectra. These extrinsic effects make the ferroelectric to paraelectric phase
transition diffuse in BZT-PT solid solutions
Stabilization of Polar Nano Regions in Pb-free ferroelectrics
Formation of polar nano regions through solid-solution additions are known to
enhance significantly the functional properties of ferroelectric materials.
Despite considerable progress in characterizing the microscopic behavior of
polar nano regions, understanding their real-space atomic structure and
dynamics of formation remains a considerable challenge. Here, using the method
of dynamic pair distribution function, we provide direct insights into the role
of solid-solution additions towards the stabilization of polar nano regions in
the Pb-free ferroelectric of Ba(Zr,Ti)O3. It is shown that for an optimum level
of substitution of Ti by larger Zr ions, the dynamics of atomic displacements
for ferroelectric polarization are slowed sufficiently, which leads to
increased local correlation among dipoles below THz frequencies. The dynamic
pair distribution function technique demonstrates unique capability to obtain
insights into locally correlated atomic dynamics in disordered materials,
including new Pb-free ferroelectrics, which is necessary to understand and
control their functional properties
Ultra-Thin CeO\u3csub\u3e2\u3c/sub\u3e Overlayer on YSZ Studied by X-Ray Surface Scattering
Transition metal catalysts such as Rh/Pt used in a three-way automotive catalytic converter have to perform reduction and oxidation functions at the same time. This can be accomplished only in a specific range of oxygen pressure and temperature. In order to maintain a constant partial pressure of oxygen in the vicinity of catalysts mixtures of ceria and zirconia are used. Ceria is an essential component due to its capability of storing oxygen under oxidizing and releasing oxygen under reducing conditions. However, this function deteriorates with time and eventually a catalytic converter stops working properly. It is not well understood why this particular mixture of oxides can achieve the role as a oxygen buffer and why its lifetime is limited. In order to address this issue and to understand the structural interplay at the ceria/zirconia interface, we studied the atomic structure of ultra-thin ceria layers deposited on single crystals of (001) oriented Y-stabilized zirconia (YSZ), in situ, during annealing in air using the synchrotron x-ray surface diffraction technique
Structure and Polarization in the High T\u3csub\u3ec\u3c/sub\u3e Ferroelectric Bi(Zn,Ti)O\u3csub\u3e3\u3c/sub\u3e-PbTiO\u3csub\u3e3\u3c/sub\u3e Solid Solutions
Theoretical ab initio and experimental methods are used to investigate the [Bi(Zn1/2Ti1/2)O3]x [PbTiO3]1-x solid solution. We find that hybridization between Zn 4s and 4p and O 2p orbitals allows the formation of short, covalent Zn-O bonds, enabling favorable coupling between A-site and B-site displacements. This leads to unusually large polarization, strong tetragonality, and an elevated ferroelectric to paraelectric phase transition temperature
Incommensurate lattice distortion in the high temperature tetragonal phase of La(Sr,Ba)CuO
We report incommensurate diffuse (ICD) scattering appearing in the
high-temperature-tetragonal (HTT) phase of La(Sr,Ba)CuO
with observed by the neutron diffraction technique. For
all compositions, a sharp superlattice peak of the low-temperature-orthorhombic
(LTO) structure is replaced by a pair of ICD peaks with the modulation vector
parallel to the CuO octahedral tilting direction, that is, the diagonal
Cu-Cu direction of the CuO plane, above the LTO-HTT transition temperature
. The temperature dependences of the incommensurability for all
samples scale approximately as , while those of the integrated intensity
of the ICD peaks scale as . These observations together with
absence of ICD peaks in the non-superconducting sample evince a
universal incommensurate lattice instability of hole-doped 214 cuprates in the
superconducting regime.Comment: 6 pages, 6 figure
Assessing environmental pollution in birds: a new methodological approach for interpreting bioaccumulation of trace elements in feather shafts using geochemical sediment data
Environmental trace element composition can have an important impact on ecosystem and population health as well individual fitness. Therefore, carefully assessing bioaccumulation of trace elements is central to studies investigating the ecological impact of pollution. Colonial birds are important bioindicators since non-invasive sampling can easily be achieved through sampling of chick feathers, which controls for some confounding factors of variability (age and environmental heterogeneity). However, an additional confounding factor, external contamination (ExCo), which remains even after washing feathers, has frequently been overlooked in the literature. We developed a new method to reliably interpret bioaccumulation of 10 trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Sn and Zn) in feathers using chicks of a colonial species: the Greater Flamingo, Phoenicopterus roseus. First, only shafts were used to remove ExCo retained in vanes. Secondly, we applied a thorough washing procedure. Thirdly, we applied a new analytical method to control for ExCo, which assumes that ExCo is mainly due to adhered sediment particles and that the relative concentration of each trace element will be similar to the sediment geochemical composition of sampling sites. We validated this new methodology by comparing trace element composition and particle composition (by scanning electron microscopy and mass spectrometry) of washed and unwashed feathers. The washing procedure removed >99% of K indicating that most of the ExCo from salt was removed. Scanning electron microscopy and mass spectrometry revealed that some sediment particles remained after washing, especially clays which are likely to severely bias bioaccumulation interpretation. We successfully controlled for ExCo by calculating the ratio of ExCo due to sediment using the geochemical fingerprint of sediment samples. Our methodology leads to conservative estimates of bioaccumulation for As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Sn and Zn. We have validated a new more reliable method of analysing trace element concentrations in feathers, which effectively controls for ExCo, if geochemical sediment data can be meaningfully compared to ExCo of feathers. We have demonstrated that overlooking ExCo leads to potentially erroneous conclusions, and we urge that the method applied in this study be considered in future studies.Peer Reviewe
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