scholarly journals Effect of chemical composition on microstructural properties and sintering kinetics of (Ba,Sr)TiO3 powders

2018 ◽  
Vol 50 (1) ◽  
pp. 29-38 ◽  
Author(s):  
D.A. Kosanovic ◽  
V.A. Blagojevic ◽  
N.J. Labus ◽  
N.B. Tadic ◽  
V.B. Pavlovic ◽  
...  
Keyword(s):  
Phase Transition ◽  
Powder Mixture ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Microstructural Properties ◽  
Sintering Process ◽  
Sintering Kinetics ◽  
Chemical Content ◽  
Higher Temperature ◽  
Activation Energy Of Sintering

Barium strontium titanate powders with different Ba:Sr ratios were investigated to determine the influence of the initial composition of powder mixture on microstructural properties and sintering kinetics. It was determined that BaCO3 and SrCO3 react differently to mixing, resulting in Ba0.5Sr0.5CO3 in the sample with 80% Ba and different contents of Ba1- xSrxTiO3 in samples with 50% and 20% Ba. In addition, the morphology is also different, with higher Sr content leading to larger particles size and less agglomeration. The different chemical content of the initial powder mixture also has a marked impact on the sintering process: the onset of sintering shifts towards higher temperature with higher Sr content, while the average apparent activation energy of sintering is the highest for the sample with 80% Ba and the lowest for the mixture with 50% Ba. In addition, hexagonal-to-cubic phase transformation was observed in parallel with the sintering process, where the position of the phase transition shifts to lower temperatures with an increase in Sr content. This is consistent with the behavior of low-temperature phase transitions of BST. The phase transition was not observed in sintered samples, suggesting that there is a size-dependence of the phase transition temperature.

scholarly journals Numerical Simulation of the Phase Transition Control in a Cylindrical Sample Made of Ferromagnetic Shape Memory Alloy

Computation ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 38
Author(s):  
Anatoli A. Rogovoy ◽  
Olga S. Stolbova
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Shape Memory ◽  
Outer Surface ◽  
Original Position ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Martensitic State ◽  
Ferromagnetic Shape Memory ◽  
The Magnetic Field

The paper considers ferromagnetic alloys, which exhibit the shape memory effect during phase transition from the high-temperature cubic phase (austenite) to the low-temperature tetragonal phase (martensite) in the ferromagnetic state. In these alloys, significant macroscopic strains are generated during the direct temperature phase transition from the austenitic to the martensitic state, provided that the process proceeds under the action of the applied mechanical stresses. The critical phase transition temperatures in such alloys depend not only on the stress fields, but also on the magnetic field. By changing the magnetic field, it is possible to control the process of phase transition. In this work, within the framework of the finite deformation theory, we develop a model that allows us to describe the process of the control of the direct (austenite-martensite) and reverse (martensite-austenite) phase transitions in ferromagnetic shape memory polycrystalline materials under the action of external force, thermal, and magnetic fields with the aid of the magnetic field. In view of the fact that the magnetic field affects the material deformation, which, in turn, changes the magnetic field, we formulated and solved a coupled boundary value problem. As an example, we considered the problem of a shift of the outer surface of a long hollow cylinder made of ferromagnetic alloy. The numerical implementation of the problem was based on the finite element method using the step-by-step loading procedure. Complete recovery of the strains accumulated during the direct phase transition and reverting of the axially-displaced outer surface of the cylinder to its original position occurred both on heating of the sample to the temperatures of the reverse phase transition and at a constant temperature, when the magnetic field previously applied in the martensitic state was removed.

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites

2001 ◽  
Vol 57 (3) ◽  
pp. 221-230 ◽  
Author(s):  
A. Guelylah ◽  
G. Madariaga ◽  
V. Petricek ◽  
T. Breczewski ◽  
M. I. Aroyo ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Mode Analysis ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
New Type ◽  
Low Temperature Phase

The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100–300 K. Using DSC measurements, a phase transition has been detected at 213 K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690 (8), b = 20.136 (2), c = 10.0329 (4) Å, γ = 90.01 (1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds.

Structural studies of schultenite in the temperature range 125–324 K by pulsed single crystal neutron diffraction — hydrogen ordering and structural distortions

1994 ◽  
Vol 58 (393) ◽  
pp. 629-634 ◽  
Author(s):  
C. C. Wilson
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Single Crystal ◽  
Heavy Atom ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
High Symmetry ◽  
Normal Behaviour ◽  
Higher Temperature ◽  
Symmetry Structure

AbstractThe structure of the mineral schultenite, PbHAsO4, has been studied using pulsed neutron single crystal diffraction. The low-temperature, low-symmetry structure is found to exhibit substantial ordering of the hydrogen atom onto one of two possible sites, which are equally occupied in the high-temperature phase above 313 K. The occupancies found at low temperature agree well with the normal behaviour for such a hydrogen ordering phase transition in this type of material. In addition the heavy atom lattice distortion has been characterised as a function of temperature and found to follow broadly the pattern of hydrogen ordering. Higher-temperature measurements at and above the phase transition confirm the high symmetry nature of the structure in this region, with no significant distortions from this within the resolution of the present data.

scholarly journals A temperature-dependent phase transformation of (E)-2-[(4-chlorophenyl)imino]acenaphthylen-1-one

2017 ◽  
Vol 73 (8) ◽  
pp. 1255-1258
Author(s):  
Lipiao Bao ◽  
Marilyn M. Olmstead
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Crystal Packing ◽  
Mirror Plane ◽  
Temperature Phase ◽  
Ordered Structure ◽  
Temperature Dependent ◽  
Reversible Phase Transition ◽  
Higher Temperature ◽  
Reversible Phase

The crystal structure determination based on 90 K data of the title imine ligand, C18H10ClNO, revealed non-merohedral twinning with three twin domains. In our experience, this is an indication of an ordering phase transition. Consequently, the structure was redetermined with higher temperature data, and a reversible phase transition was discovered. The higher temperature phase is indeed an ordered structure. At the higher temperature, the 4-chlorophenyl group has rotated by ca 7° into a crystallographic mirror plane. Warming the crystal from 90 K to 250 K changes the space group from triclinic P-1, to monoclinic P21/m. Diverse non-classical interactions are present in the crystal packing, and these are described for the phase change reported in this work. The crystal structure of the title imine ligand, measured at 100 K, has been reported on previously [Kovach et al. (2011). J. Mol. Struct. 992, 33–38].

High-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type PbTiO3phases

2016 ◽  
Vol 72 (3) ◽  
pp. 381-388 ◽  
Author(s):  
Akira Yoshiasa ◽  
Tomotaka Nakatani ◽  
Akihiko Nakatsuka ◽  
Maki Okube ◽  
Kazumasa Sugiyama ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Single Crystal ◽  
Diffraction Study ◽  
Relative Displacement ◽  
High Temperature Phase ◽  
Cubic Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray

A high-temperature single-crystal X-ray diffraction study of a synthetic PbTiO3perovskite was carried out over the wide temperature range 298–928 K. A transition from a tetragonal (P4mm) to a cubic (Pm \bar 3 m) phase has been revealed near 753 K. In the non-centrosymmetricP4mmsymmetry group, the difference in relative displacement between Pb and O along thec-axis is much larger than that between Ti and O. The Pb and Ti cations contribute sufficiently to polarization being shifted in the opposite direction compared with the shift of O atoms. Deviation from the linear changes in Debye–Waller factors and bonding distances in the tetragonal phases can be interpreted as a precursor phenomenon before the phase transition. Disturbance of the temperature factorUeqfor O is observed in the vicinity of the transition point, whileUeqvalues for Pb and Ti are continuously changing with increasing temperature. The O site includes the clear configurational disorder in the cubic phase. The polar local positional distortions remain in the cubic phase and are regarded as the cause of the paraelectricity. Estimated values of the Debye temperature ΘDfor Pb and Ti are 154 and 467 K in the tetragonal phase and decrease 22% in the high-temperature phase. Effective potentials for Pb and Ti change significantly and become soft after the phase transition.

Synthesis, characterization and phase transitions in the inorganic–organic layered perovskite-type hybrids [(C n H2n + 1NH3)2PbI4], n = 4, 5 and 6

2007 ◽  
Vol 63 (5) ◽  
pp. 735-747 ◽  
Author(s):  
David G. Billing ◽  
Andreas Lemmerer
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Layered Perovskite ◽  
Temperature Phase ◽  
Two Phase ◽  
Structural Details ◽  
Temperature Phase Transition ◽  
Higher Temperature ◽  
First Order Phase ◽  
Perovskite Type

Three inorganic–organic layered perovskite-type hybrids of the general formula [(C n H2n + 1NH3)2PbI4], n = 4, 5 and 6, display a number of reversible first-order phase transitions in the temperature range from 256 to 393 K. [(C4H9NH3)2PbI4] has a single phase transition, [(C5H11NH3)2PbI4] has two phase transitions and [(C6H13NH3)2PbI4] has three phase transitions. In all three cases, the lowest-temperature phase transition is thermochromic and the crystals change colour from yellow in their lowest-temperature phase to orange in their higher-temperature phase for [(C4H9NH3)2PbI4] and [(C6H13NH3)2PbI4], and from orange to red for [(C5H11NH3)2PbI4]. The structural details associated with this phase transition have been investigated via single-crystal X-ray diffraction, SC-XRD, for all three compounds.

Temperature Correction for Ceramic Powder X-Ray Diffraction at a Higher Temperature

2013 ◽  
Vol 718-720 ◽  
pp. 768-772 ◽  
Author(s):  
Da Yong Lu ◽  
Wei Cheng ◽  
Peng Yuan Chen ◽  
Xiu Yun Sun
Keyword(s):  
Phase Transition ◽  
Ceramic Powder ◽  
Thermal Relaxation ◽  
Temperature Correction ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Characteristic Peak ◽  
X Ray ◽  
Linear Dependency ◽  
Higher Temperature

For powder XRD measurement at a higher temperature, there is a great difference (ΔT) between the temperature (T) detected by a thermocouple in a specimen stage and the actual temperature (Ta) of the ceramic powder surface irradiated by X-ray. The BaTiO3 ceramic powder was employed to make an temperature correction on heating in light of the change of the ~ 45º characteristic peak in the vicinity of its tetragonal-cubic phase transition point (TC = 130 °C). The thermal relaxation of BaTiO3 is considered. When the BaTiO3 ceramic powder was measured at TC, the phase transition occurred at T = 170 °C and ΔT was determined as 40 °C, which is 10 °C higher than that of the ceramic bulk. The error of temperature correction is less than ± 3 °C at TC. The approximation of a linear dependency Ta - T was given as a temperature correction line between 25 and 130 °C (Ta here).

Reconstructive phase transition in (NH4)3TiF7accompanied by the ordering of TiF6octahedra

2014 ◽  
Vol 70 (6) ◽  
pp. 924-931 ◽  
Author(s):  
Maxim Molokeev ◽  
S. V. Misjul ◽  
I. N. Flerov ◽  
N. M. Laptash
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Room Temperature ◽  
Parent Phase ◽  
High Temperature Phase ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Large Rotations ◽  
Fourfold Axis

An unusual phase transitionP4/mnc→ Pa\bar 3 has been detected after cooling the (NH4)3TiF7compound. Some TiF6octahedra, which are disordered in the room-temperature tetragonal structure, become ordered in the low-temperature cubic phase due to the disappearance of the fourfold axis. Other TiF6octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.5–1.8 Å that implies a reconstructive phase transition. It was supposed that phasesP4/mbmand Pm\bar 3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm\bar 3m →P4/mbm→P4/mnc→ Pa\bar 3. The interrelation between (NH4)3TiF7, (NH4)3GeF7and (NH4)3PbF7is found, which allows us to suppose phase transitions in relative compounds.

Isostructural phase transition in m-carboxyphenylammonium monohydrogenphosphite

2005 ◽  
Vol 61 (6) ◽  
pp. 700-709 ◽  
Author(s):  
El-Eulmi Bendeif ◽  
Slimane Dahaoui ◽  
Michel François ◽  
Nourredine Benali-Cherif ◽  
Claude Lecomte
Keyword(s):  
Phase Transition ◽  
Reciprocal Lattice ◽  
Forthcoming Paper ◽  
Unit Cell ◽  
Temperature Phase ◽  
Data Sets ◽  
Scanning Calorimetry ◽  
Cell Parameters ◽  
Higher Temperature ◽  
Lower Temperature

Crystals of m-carboxyphenylammonium monohydrogenphosphite, C7H8NO_{2}^+·H2PO_3^{-} (m-CPAMP), space group P2_{1}/c, grown from aqueous solution undergo a reversible first-order single-crystal phase transition at Tc = 246 (2) K with a hysteresis of 3.6 K. The thermal behaviour of the sample was characterized by differential scanning calorimetry (DSC) experiments. Variations of the unit-cell parameters versus temperature between 100 and 320 K are reported. The transition from the higher-temperature phase (HTP) to the lower-temperature phase (LTP) is characterized by a unit-cell volume contraction of 1.77%. The average structure and unit-cell packing of m-CPAMP at lower temperature (100 K) are reported from accurate X-ray data sets and compared with those of the higher-temperature phase (293 K) in order to investigate the mechanism of the phase transition. The reciprocal lattice reconstruction showed a few very weak satellite reflections which will be discussed in a forthcoming paper.

The square-planar to flattened-tetrahedral CuX42−(X= Cl, Br) structural phase transition in 1,2,6-trimethylpyridinium salts

2015 ◽  
Vol 71 (1) ◽  
pp. 48-60 ◽  
Author(s):  
Annette Kelley ◽  
Sowjanya Nalla ◽  
Marcus R. Bond
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
Hydrogen Bonding ◽  
Low Temperature ◽  
Structural Phase ◽  
Temperature Phase ◽  
Tetrahedral Geometry ◽  
Square Planar ◽  
Higher Temperature ◽  
Low Temperature Phase

The abrupt green-to-yellow thermochromism observed for certainA2CuCl4compounds has long been attributed to the presence of strong N—H hydrogen bonding in the low-temperature phase that favors square-planar CuCl42−(green in color) through reduction of ligand–ligand repulsion. Weakening of the hydrogen bonding at higher temperature results in the transformation to (far more common) flattened-tetrahedral geometry – the expected geometry for CuBr42−complexes due to their greater ligand–ligand repulsion. The square-planar to flattened-tetrahedral transitions in (1,2,6-trimethylpyridinium)2CuX4provide the first examples of this phase transformation in the absence of N—H hydrogen bonding and for a CuBr42−complex. These results suggest that the square-planar to flattened-tetrahedral transformation in CuX42−systems may be more common than previously thought.

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