The Ion Conducting Properties of Perovskite-Type Solid Solutions (La0.5Li0.5) [Ti1-x(M0.5Nb0.5)x]O3 (M = Al, Ga)

2006 ◽  
Vol 514-516 ◽  
pp. 407-411 ◽  
Author(s):  
Elena A. Fortalnova ◽  
Alexander V. Mosunov ◽  
Marina G. Safronenko ◽  
Nikolay U. Venskovskii ◽  
Ekaterina D. Politova
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Cell Volume ◽  
Solid Solutions ◽  
Unit Cell Volume ◽  
Relaxation Effect ◽  
Unit Cell ◽  
Temperature Dependences ◽  
Ion Conducting ◽  
Perovskite Type

The influence of B-site substitution on electroconducting properties of perovskite-type solid solutions (La0.5Li0.5)[Ti1-x(M0.5Nb0.5)x]O3 with M = Al, Ga, have been studied. A decrease in the conductivity due to the unit cell contraction with increasing x in case of M = Al has been revealed. In case of Ga and Nb substitutions for Ti the unit cell volume has been found to increase with increasing x while the conductivity decreases due to the impurity phases presence. The high and low temperature anomalies on the temperature dependences of dielectric characteristic related to both the relaxation effect and phase transitions have been revealed.

Oxygen stoichiometry, unit cell volume, and thermodynamic quantities of perovskite-type oxides

2006 ◽  
Vol 11 (4) ◽  
pp. 469-477 ◽  
Author(s):  
Egle Girdauskaite ◽  
Helmut Ullmann ◽  
Mahmoud Al Daroukh ◽  
Vladimir Vashook ◽  
Martin Bülow ◽  
...  
Keyword(s):  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Oxygen Stoichiometry ◽  
Thermodynamic Quantities ◽  
Perovskite Type

Atomic displacements at and order of all phase transitions in multiferroic YMnO3 and BaTiO3

2009 ◽  
Vol 65 (4) ◽  
pp. 450-457 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Landau Theory ◽  
Unit Cell ◽  
Paramagnetic Phase ◽  
First Order ◽  
Atomic Displacements ◽  
Magnetic Symmetry

Coordinate analysis of the multiple phase transitions in hexagonal YMnO3 leads to the prediction of a previously unknown aristotype phase, with the resulting phase-transition sequence: P63′cm′(e.g.) ↔ P63 cm ↔ P63/mcm ↔ P63/mmc ↔ P6/mmm. Below the Néel temperature T N ≃ 75 K, the structure is antiferromagnetic with the magnetic symmetry not yet determined. Above T N the P63 cm phase is ferroelectric with Curie temperature T C ≃ 1105 K. The nonpolar paramagnetic phase stable between T C and ∼ 1360 K transforms to a second nonpolar paramagnetic phase stable to ∼ 1600 K, with unit-cell volume one-third that below 1360 K. The predicted aristotype phase at the highest temperature is nonpolar and paramagnetic, with unit-cell volume reduced by a further factor of 2. Coordinate analysis of the three well known phase transitions undergone by tetragonal BaTiO3, with space-group sequence R3m ↔ Amm2 ↔ P4mm ↔ Pm\overline 3m, provides a basis for deriving the aristotype phase in YMnO3. Landau theory allows the I ↔ II, III ↔ IV and IV ↔ V phase transitions in YMnO3, and also the I ↔ II phase transition in BaTiO3, to be continuous; all four, however, unambiguously exhibit first-order characteristics. The origin of phase transitions, permitted by theory to be second order, that are first order instead have not yet been thoroughly investigated; several possibilities are briefly considered.

Cell volumes of LaPO4–CePO4 solid solutions

1987 ◽  
Vol 20 (4) ◽  
pp. 319-320 ◽  
Author(s):  
R. S. de Biasi ◽  
A. A. R. Fernandes ◽  
J. C. S. Oliveira
Keyword(s):  
Cell Volume ◽  
Solid Solutions ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Cube Root ◽  
Lattice Constants ◽  
Vegard’S Law ◽  
Cell Volumes

Lattice constants have been determined for solid solutions of the form La x Ce1−x PO4. A plot of the cube root of the unit-cell volume as a function of x shows that this system follows Végard's law.

Squeezing electrons out of 6s2 lone-pairs in perovskite-type oxides

2019 ◽  
Vol 55 (27) ◽  
pp. 3887-3890
Author(s):  
Chun-Hai Wang ◽  
Paula Kayser ◽  
Brendan J. Kennedy ◽  
Helen E. Maynard-Casely ◽  
Qinfen Gu ◽  
...  
Keyword(s):  
Cell Volume ◽  
Unit Cell Volume ◽  
Applied Pressure ◽  
Unit Cell ◽  
Lone Pairs ◽  
Volume Collapse ◽  
Perovskite Type

Unit cell volume collapse in Ba2BiRuO6, Ba2BiIrO6 and Ba2BiOsO6 when Bi(iii) is oxidised to Bi(v) by external applied pressure.

A low-temperature polymorph ofm-quinquephenyl

2012 ◽  
Vol 68 (12) ◽  
pp. o492-o497 ◽  
Author(s):  
Ligia R. Gomes ◽  
R. Alan Howie ◽  
John Nicolson Low ◽  
Ana S. M. C. Rodrigues ◽  
Luís M. N. B. F. Santos
Keyword(s):  
Low Temperature ◽  
Cell Volume ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Geometric Parameters ◽  
Asymmetric Unit ◽  
Cell Axis ◽  
Space Group ◽  
Π Interactions

A low-temperature polymorph of 1,1′:3′,1′′:3′′,1′′′:3′′′,1′′′′-quinquephenyl (m-quinquephenyl), C30H22, crystallizes in the space groupP21/cwith two molecules in the asymmetric unit. The crystal is a three-component nonmerohedral twin. A previously reported room-temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993).Chem. Commun.pp. 1795–1797] also crystallizes with two molecules in the asymmetric unit in the space groupP\overline{1}. The unit-cell volume for the low-temperature polymorph is 4120.5 (4) Å3, almost twice that of the room-temperature polymorph which is 2102.3 (6) Å3. The molecules in both structures adopt a U-shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit-cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C—H...π interactions.

The Effect of Substituting Ga for Alon Crystal Structure of Phosphors MAl 2Si2O8: Eu2+ (M= Ca, Sr, Ba)

2022 ◽  
Vol 905 ◽  
pp. 91-95
Author(s):  
Fei Wang ◽  
Hui Hui Chen ◽  
Shi Wei Zhang
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Cell Volume ◽  
Solid Solutions ◽  
Solid State Reaction ◽  
Unit Cell Volume ◽  
Lattice Parameter ◽  
Unit Cell ◽  
Lattice Parameters ◽  
Reductive Atmosphere

A series of luminescence phosphors M0.955Al2 –xGaxSi2O8∶Eu2+ (M=Ca, Sr, Ba, x = 0~1.0) were prepared via solid-state reaction in weak reductive atmosphere. The lattice positions were discussed. It was found that when Ga3+ entered MAl2Si2O8 lattice and substituted Al3+, complete solid solutions formed. The lattice parameters (a, b, c) and unit cell volume of phosphors M 0.955Al2 –xGaxSi2O8: Eu2+ (M=Ca, Sr, Ba, x = 0~1.0) increased linearly, the lattice parameters (α, β,γ) of Ca0.955Al2–xGaxSi2O8∶Eu2+(CAS) decreased linearly and the lattice parameter β of Sr0.955Al2–xGaxSi2O8∶Eu2+(SAS) and Ba0.955Al2–xGaxSi2O8∶Eu2+(BAS) increased linearly as Ga3+ content increased.

scholarly journals Allanite at high temperature: effect of REE on the thermal behaviour of epidote-group minerals

2021 ◽  
Vol 48 (9) ◽  
Author(s):  
G. Diego Gatta ◽  
Francesco Pagliaro ◽  
Paolo Lotti ◽  
Alessandro Guastoni ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Cell Volume ◽  
Thermal Behaviour ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Atomic Scale ◽  
Elastic Behaviour ◽  
Positive Trend ◽  
Cell Parameters ◽  
Thermal Anisotropy ◽  
Different Temperatures

AbstractThe thermal behaviour of a natural allanite-(Ce) has been investigated up to 1073 K (at room pressure) by means of in situ synchrotron powder X-ray diffraction and single-crystal neutron diffraction. Allanite preserves its crystallinity up to 1073 K. However, up to 700 K, the thermal behaviour along the three principal crystallographic axes, of the monoclinic β angle and of the unit-cell volume follow monotonically increasing trends, which are almost linear. At T > 700–800 K, a drastic change takes place: an inversion of the trend is observed along the a and b axes (more pronounced along b) and for the monoclinic β angle; in contrast, an anomalous increase of the expansion is observed along the c axis, which controls the positive trend experienced by the unit-cell volume at T > 700–800 K. Data collected back to room T, after the HT experiments, show unit-cell parameters significantly different with respect to those previously measured at 293 K: allanite responds with an ideal elastic behaviour up to 700 K, and at T > 700–800 K its behaviour deviates from the elasticity field. The thermo-elastic behaviour up to 700 K was modelled with a modified Holland–Powell EoS; for the unit-cell volume, we obtained the following parameters: VT0 = 467.33(6) Å3 and αT0(V) = 2.8(3) × 10–5 K−1. The thermal anisotropy, derived on the basis of the axial expansion along the three main crystallographic directions, is the following: αT0(a):αT0(b):αT0(c) = 1.08:1:1.36. The T-induced mechanisms, at the atomic scale, are described on the basis of the neutron structure refinements at different temperatures. Evidence of dehydroxylation effect at T ≥ 848 K are reported. A comparison between the thermal behaviour of allanite, epidote and clinozoisite is carried out.

scholarly journals Study of Structural, Magnetic, and Mossbauer Properties of Dy2Fe16Ga1−xNbx (0.0 ≤ x ≤ 1.0) Prepared via Arc Melting Process

2021 ◽  
Vol 7 (3) ◽  
pp. 42
Author(s):  
Jiba N. Dahal ◽  
Kalangala Sikkanther Syed Ali ◽  
Sanjay R. Mishra
Keyword(s):  
Isomer Shift ◽  
Cell Volume ◽  
Intermetallic Compounds ◽  
Unit Cell Volume ◽  
Rietveld Analysis ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Arc Melting ◽  
Nb Content

Intermetallic compounds of Dy2Fe16Ga1−xNbx (x = 0.0 to 1.00) were synthesized by arc melting. Samples were investigated for structural, magnetic, and hyperfine properties using X-ray diffraction, vibration sample magnetometer, and Mossbauer spectrometer, respectively. The Rietveld analysis of room temperature X-ray diffraction data shows that all the samples were crystallized in Th2Fe17 structure. The unit cell volume of alloys increased linearly with an increase in Nb content. The maximum Curie temperature Tc ~523 K for x = 0.6 sample is higher than Tc = 153 K of Dy2Fe17. The saturation magnetization decreased linearly with increasing Nb content from 61.57 emu/g for x = 0.0 to 42.46 emu/g for x = 1.0. The Mössbauer spectra and Rietveld analysis showed a small amount of DyFe3 and NbFe2 secondary phases at x = 1.0. The hyperfine field of Dy2Fe16Ga1−xNbx decreased while the isomer shift values increased with the Nb content. The observed increase in isomer shift may have resulted from the decrease in s electron density due to the unit cell volume expansion. The substantial increase in Tc of thus prepared intermetallic compounds is expected to have implications in magnets used for high-temperature applications.

Mössbauer Studies of Fe2+ in Iron Langbeinites and other Crystals with Langbeinite Structure

1998 ◽  
Vol 53 (1-2) ◽  
pp. 27-37 ◽  
Author(s):  
M. Windhaus ◽  
B. D. Mosel ◽  
W. Müller-Warmuth
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Low Temperature ◽  
High Spin State ◽  
Cubic Phases ◽  
Debye Temperatures ◽  
Phase Transition Temperatures ◽  
Abrupt Changes ◽  
Temperature Dependences

Abstract 57 Fe Mössbauer spectra have been measured at various temperatures between 4.2 K and 300 K for iron langbeinites A 2 Fe 2^04)3 with A = K, NH 4 , Rb, T1 and magnesium, manganese and cadmium lang-beinites doped with Fe" + . The spectra revealed several contributions whose isomer shifts and quadru-pole splittings have been obtained by fitting program routines. For the high-temperature cubic phases two crystallographically non-equivalent iron sites have been identified, characteristic of Fe2+ in the high-spin state. Abrupt changes of the quadrupole couplings indicated phase transitions; in some cases, the spectra have also revealed several sites for Fe2+ in low temperature phases. From the temperature dependences, phase transition temperatures, crystal field splittings and Debye temperatures have been derived.

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