scholarly journals Synthesis ofβ-Phase (Bi2O3)1-x(Dy2O3)x(0.01

2007 ◽  
Vol 2007 ◽  
pp. 1-5 ◽  
Author(s):  
Serdar Yilmaz ◽  
Orhan Turkoglu ◽  
Ibrahim Belenli
Keyword(s):  
Phase Transition ◽  
Electrical Conductivity ◽  
Ionic Conductivity ◽  
Doping Concentration ◽  
Unit Cell Parameters ◽  
Oxygen Conductivity ◽  
Cell Parameters ◽  
Conductivity Curve ◽  
Phase Systems ◽  
Regular Increase

β-phase (Bi2O3)1-x(Dy2O3)xsystem with tetragonal structure is synthesized for0.01<x<0.10molar doping. Unit cell parameters increased with increasing the doping. We have studied the dependence of total electrical conductvity on temperature, doping concentration ofβ-phase systems. The phase transition which manifests itself by the jump in the conductivity curve was also verified by DTA and both measurements are rather compatible. The electrical conductivity curves ofβ-phase structure revealed regular increase in the form of an Arrhenius curve. The activation energies are calculated from these graphs.Bi2O3-basedDy2O3doped ceramics show ionic oxygen conductivity. The conductivity increased as the doping concentration increased. The highest value of conductivity is 0.006 0.006ohm-1cm-1(600∘C)for theβ-phase (Bi2O3)0.91(Dy2O3)0.09(800∘C). The sample with the highest conductivity is (Bi2O3)0.91(Dy2O3)0.09(800∘C)binary system where 1.450 ohm−1cm−1(745∘C).

Monoclinic-to-orthorhombic phase transition in Cu2(AsO4)(OH) olivenite at high temperature: strain and mode decomposition analyses

2018 ◽  
Vol 82 (2) ◽  
pp. 347-365 ◽  
Author(s):  
Serena C. Tarantino ◽  
Michele Zema ◽  
Athos M. Callegari ◽  
Massimo Boiocchi ◽  
Michael A. Carpenter
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Single Crystal ◽  
Volume Expansion ◽  
Monoclinic Phase ◽  
Orthorhombic Phase ◽  
Unit Cell ◽  
The Other ◽  
Unit Cell Parameters ◽  
Cell Parameters

ABSTRACTA natural olivenite single crystal was submitted to in situ high-temperature single-crystal X-ray diffraction from room temperature (RT) to 500°C. Unit-cell parameters were measured at regular intervals of 25°C, and complete datasets collected at T = 25, 50, 100, 150, 200, 250, 300, 400 and 500°C. Evolution of unit-cell parameters and structure refinements indicates that olivenite undergoes a structural phase transition from P21/n to Pnnm at ~200°C, and eventually becomes isostructural with the other members of the olivenite-mineral group. Volume expansion with temperature is larger in the monoclinic phase – where it follows a non-linear trend – than in the orthorhombic one. Axial and volume expansion coefficients of the orthorhombic olivenite phase are positive and linear and similar to those of the other Cu-bearing member of the mineral family, namely libethenite, but rather different from those of the Zn-analogue arsenate adamite.Distortion of Cu polyhedra is quite high in the olivenite monoclinic phase at RT and goes towards a relative regularization with increasing T until the phase transition occurs. In the orthorhombic phase, no significant variation of the polyhedral distortion parameters is observed with increasing temperature, and maximum expansion is along the b direction and governed by corner-sharing. Landau potential provides a good representation of the macroscopic changes associated with the phase transition, coupling between the strains and the order parameter is responsible for the nearly tricritical character of the transition.

Origin of ferroelectric phase transition in SbSClxI1-x mixed crystals

2014 ◽  
Vol 28 (30) ◽  
pp. 1450209 ◽  
Author(s):  
A. Audzijonis ◽  
L. Žigas ◽  
R. Sereika ◽  
R. Žaltauskas
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Temperature Dependence ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Harmonic Approximation ◽  
Temperature Dependent ◽  
Normal Coordinate ◽  
Unit Cell Parameters ◽  
Cell Parameters

The measurements of SbSCl x I 1-x(x = 0.2) temperature dependent capacitance were carried out. The temperature of ferroelectric phase transition TC ≈340 K was measured experimentally. TC of SbSCl x I 1-x was calculated theoretically in anharmonic and harmonic approximations. TC was calculated in anharmonic approximation using temperature dependence of mean potential energy of Sb atoms as a function of the soft B1u symmetry normal coordinate along c(z)-axis. Moreover, TC was calculated in harmonic approximation using temperature dependence of vibrational thermodynamic functions (Helmholc free energy). TC dependence from unit cell parameters a, b and from mixture composition x was carried out.

Two phases of {[CsPH(η6-2,4,6- t Bu3C6H2)]2(η3-toluene)0.5} x : their structures and interconversions

2000 ◽  
Vol 56 (2) ◽  
pp. 210-214
Author(s):  
Thomas E. Concolino ◽  
Kin-Chung Lam ◽  
Ilia A. Guzei ◽  
Arnold L. Rheingold ◽  
Gerd W. Rabe
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Unit Cell Volume ◽  
Structural Features ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Disorder Phase Transition ◽  
Two Phases ◽  
A Minor

The solvent-bridged caesium phosphide {[CsPH(η 6-2,4,6- t Bu3C6H2)]2(η 3-toluene)0.5} x , catena-[(μ-η3-toluene)-bis[caesium(2,4,6-tri-tert-butylphenylphosphide)]], undergoes a reversible solid-state, order–disorder phase transition characterized by the doubling of the unit-cell volume at low temperature achieved by doubling one unit-cell vector. The unit-cell parameters at 293 (2) K (form A) are: a = 11.147 (4), b = 14.615 (4), c = 14.806 (5) Å, α = 70.57 (3), β = 71.85 (3), γ = 72.93 (2)°, V = 2112.5 (12) Å3, Z = 2, ρcalc = 1.362 g cm−3, R 1 = 0.0513 for 5462 reflections, wR 2 = 0.0947 for all data. The unit-cell parameters at 173 (2) K (form B) are: a = 14.6241 (3), b = 14.7393 (3), c = 22.0720 (4) Å, α = 72.2117 (7), β = 73.3659 (8), γ = 70.2953 (7)°, V = 4174.8 (2) Å3, Z = 4, ρcalc = 1.379 g cm−3, R 1 = 0.0405 for 14 010 reflections, wR 2 = 0.1326 for all data. With a minor change, the key structural features discussed previously for form A [Rabe et al. (1998). Inorg. Chem. 37, 4235–4245] remain unchanged. The η 3-toluene ligand is observed to be disordered at 293 (2) K and ordered at 173 (2) K, with the order–disorder phase transition occurring at approximately 278 (2) K.

K2(NbO)2Si4O12: a new ferroelectric

1999 ◽  
Vol 32 (3) ◽  
pp. 421-425 ◽  
Author(s):  
M. C. Foster ◽  
D. J. Arbogast ◽  
P. Photinos ◽  
R. M. Nielson ◽  
S. C. Abrahams
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Paraelectric Phase ◽  
Strong Indication ◽  
Unit Cell Parameters ◽  
Thermal Dependence ◽  
Space Group ◽  
Cell Parameters ◽  
Expansion Coefficients ◽  
Atomic Coordinates

The atomic coordinates of K2(NbO)2Si4O12reported in space groupP4bmsatisfy the structural criteria for ferroelectricity. The estimated phase-transition temperature,Tc= 2230 (250) K, is substantially in excess ofTmelting= 1476 (5) K; the hypothetical paraelectric phase in space groupP4/mbmis hence experimentally inaccessible. A strong indication that the phase transition does not occur atT<Tmeltingis provided by the absence of both calorimetric and dielectric permittivity anomalies belowTmelting, the linear thermal dependence of unit-cell parameters with expansion coefficients α11= –0.53 (12) × 10–6and α33= 24.66 (11) × 10–6 K–1between 5 and 843 K, and the generation of second harmonics between 300 and 1353 K. Demonstration of dielectric hysteresis under both direct and alternating current, with spontaneous polarizationPs≃ 0.2 C m–2, provides unambiguous verification of the ferroelectric property.

Electrical Conductivity in (Gdl-xCax)2Sn2O7±δ Pyrochlore System

1994 ◽  
Vol 369 ◽  
Author(s):  
Tae-Hwan Yu ◽  
Harry L. Tuller
Keyword(s):  
Electrical Conductivity ◽  
Ionic Conductivity ◽  
Oxygen Vacancy ◽  
Doping Concentration ◽  
Migration Energy ◽  
Conductivity Measurements ◽  
Ca Doping ◽  
Pyrochlore Compounds ◽  
Cation Radius ◽  
High Level

AbstractElectrical conductivity measurements were performed on Gd2Sn207 as a function of temperature, P02 and Ca doping concentration. An effective frenkel constant and oxygen vacancy mobility were derived. The high level of intrinsic anion disorder found in this study is consistent with expectations based on the cation radius ratio (rA/rB) which was earlier found to be important in determining anion disorder in A2B207 pyrochlore compounds [1]. The magnitude of the ionic conductivity in Gd2Sn2O7 was found to be depressed relative to Gd2(Til-xZrx)207 based systems due to a high oxygen vacancy migration energy.

Barium hollandite-type compounds BaxFe2xTi8−2xO16 with x=1.143 and 1.333

1999 ◽  
Vol 14 (1) ◽  
pp. 31-35 ◽  
Author(s):  
J. M. Loezos ◽  
T. A. Vanderah ◽  
A. R. Drews
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Framework Structure ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Acta Crystallogr

Experimental X-ray powder diffraction patterns and refined unit cell parameters for two barium hollandite-type compounds, BaxFe2xTi8−2xO16, with x=1.143 and 1.333, are reported here. Compared to the tetragonal parent structure, both compounds exhibit monoclinic distortions that increase with Ba content [Ba1.333Fe2.666Ti5.334O16: a=10.2328(8), b=2.9777(4), c=9.899(1) Å, β=91.04(1)°, V=301.58(5) Å3, Z=1, ρcalc=4.64 g/cc; Ba1.143Fe2.286Ti5.714O16: a=10.1066(6), b=2.9690(3), c=10.064(2) Å, β=90.077(6)°, V=301.98(4) Å3, Z=1, ρcalc=4.48 g/cc]. The X-ray powder patterns for both phases contain a number of broad, weak superlattice peaks attributed to ordering of the Ba2+ ions within the tunnels of the hollandite framework structure. According to the criteria developed by Cheary and Squadrito [Acta Crystallogr. B 45, 205 (1989)], the observed positions of the (0k1)/(1k0) superlattice peaks are consistent with the nominal x-values of both compounds, and the k values calculated from the corresponding d-spacings suggest that the Ba ordering within the tunnels is commensurate for x=1.333 and incommensurate for x=1.143. High-temperature X-ray diffraction data indicate that the x=1.333 compound undergoes a monoclinic→tetragonal phase transition between 310 and 360 °C.

Structure of and electron density in RbTiOAsO4 at 9.6 K

1999 ◽  
Vol 55 (5) ◽  
pp. 712-720 ◽  
Author(s):  
Jenni Almgren ◽  
Victor A. Streltsov ◽  
Alexander N. Sobolev ◽  
Brian N. Figgis ◽  
Jörgen Albertsson
Keyword(s):  
Phase Transition ◽  
Electron Density ◽  
Room Temperature ◽  
Ferroelectric Properties ◽  
Polarization Vector ◽  
Difference Electron Density ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Structure Factors ◽  
The Difference

Structure factors for rubidium titanyl arsenate, RbTiOAsO4, were measured with Mo Kα radiation (λ = 0.71069 Å) at 9.6 and 295 K. The data show that there is no phase transition between room temperature and 9.6 K. The space group is Pna2 1. Unit-cell parameters are a = 13.218 (1), b = 6.6500 (9) and c = 10.761 (1) Å at 9.6 K, and a = 13.261 (2), b = 6.6791 (8) and c = 10.769 (1) Å at 295 K. As the temperature was lowered from 295 to 9.6 K the Rb atoms moved along the c axis in the direction of the polarization vector, while no significant change was noted for the Ti–O–As network. Strong accumulation and polarization of the difference electron density (Δρ) in exceptionally short covalent Ti—O bonds alternates with the depleted density in long Ti—O bonds. The Δρ near the Ti atoms is polarized and aligned in the negative c direction in accordance with the ferroelectric properties of this material. However, the electron density near the Rb atoms is depleted in this direction and the excess Δρ is moved further away from the nuclei along the c vector.

scholarly journals Electrical conductivity of the ionic conductor tetragonal (Bi2O3)1-x(Eu2O3)x

Cerâmica ◽  
2011 ◽  
Vol 57 (342) ◽  
pp. 185-192 ◽  
Author(s):  
S. Yilmaz ◽  
O. Turkoglu ◽  
M. Ari ◽  
I. Belenli
Keyword(s):  
Phase Transition ◽  
Thermal Analysis ◽  
Electrical Conductivity ◽  
Differential Thermal Analysis ◽  
Doping Concentration ◽  
Binary Systems ◽  
Ionic Conductor ◽  
Probe Technique ◽  
Β Phase ◽  
Concentration Dependences

Electrical conductivity of tetragonal β-phase (Bi2O3)1-x(Eu2O3)x (0.01 ≤ x ≤ 0.10 %mol) ceramic systems were investigated. The temperature and doping concentration dependences of the electrical conductivity were studied by four-point probe technique. The electrical conductivity increases with the increasing doping concentration and temperature. The highest value of the electrical conductivity is 0.013 Ω-1cm-1 (x = 0.05, 750 ºC) for the β-phase at 670 ºC and 0.57 Ω-1cm-1 (x=0.05, 800 ºC) in binary systems at 690 ºC. The phase transition which manifests itself by the jump in the conductivity curves was seen and verified by differential thermal analysis measurements. The activation energies of the samples were found to be about 0.71-1.57 eV.

Kinematical and Dynamical CBED Pattern Models: Increasing the Accuracy of the Unit-Cell Parameter Measurements Based on CBED Patterns

1990 ◽  
Vol 48 (2) ◽  
pp. 540-541
Author(s):  
I.N. Yadhikov ◽  
S.K. Maksimov
Keyword(s):  
Reciprocal Lattice ◽  
Unit Cell ◽  
Reciprocal Lattice Vector ◽  
Unit Cell Parameters ◽  
Lattice Vector ◽  
Cell Parameters ◽  
Accuracy Of Measurements ◽  
The Difference ◽  
Image Position ◽  
Convergent Beam

Convergent beam electron diffraction (CBED) is widely used as a microanalysis tool. By the relative position of HOLZ-lines (Higher Order Laue Zone) in CBED-patterns one can determine the unit cell parameters with a high accuracy up to 0.1%. For this purpose, maps of HOLZ-lines are simulated with the help of a computer so that the best matching of maps with experimental CBED-pattern should be reached. In maps, HOLZ-lines are approximated, as a rule, by straight lines. The actual HOLZ-lines, however, are different from the straights. If we decrease accelerating voltage, the difference is increased and, thus, the accuracy of the unit cell parameters determination by the method becomes lower.To improve the accuracy of measurements it is necessary to give up the HOLZ-lines substitution by the straights. According to the kinematical theory a HOLZ-line is merely a fragment of ellipse arc described by the parametric equationwith arc corresponding to change of β parameter from -90° to +90°, wherevector, h - the distance between Laue zones, g - the value of the reciprocal lattice vector, g‖ - the value of the reciprocal lattice vector projection on zero Laue zone.

Sectioned rubisco crystals in TEM

1990 ◽  
Vol 48 (3) ◽  
pp. 664-665
Author(s):  
Gunnel Karlsson ◽  
Jan-Olov Bovin ◽  
Michael Bosma
Keyword(s):  
Plant Cell ◽  
Carbon Fixation ◽  
Unit Cell ◽  
Protein Crystals ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Photosynthetic Carbon Fixation ◽  
Photosynthetic Carbon

RuBisCO (D-ribulose-l,5-biphosphate carboxylase/oxygenase) is the most aboundant enzyme in the plant cell and it catalyses the key carboxylation reaction of photosynthetic carbon fixation, but also the competing oxygenase reaction of photorespiation. In vitro crystallized RuBisCO has been studied earlier but this investigation concerns in vivo existance of RuBisCO crystals in anthers and leaves ofsugarbeets. For the identification of in vivo protein crystals it is important to be able to determinethe unit cell of cytochemically identified crystals in the same image. In order to obtain the best combination of optimal contrast and resolution we have studied different staining and electron accelerating voltages. It is known that embedding and sectioning can cause deformation and obscure the unit cell parameters.

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