Structure and Phase Transition of [(CH2OH)3CNH3]2SiF6

2003 ◽  
Vol 58 (2-3) ◽  
pp. 121-125 ◽  
Author(s):  
B. Kosturek ◽  
Z. Czapla ◽  
A. Waskowska
Keyword(s):  
Phase Transition ◽  
Optical Observations ◽  
Linear Birefringence ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Dsc Measurements ◽  
First Order Phase Transition ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
First Order Phase

Single crystals of (TRIS)2SiF6 were grown and characterised by X-ray analysis, differential scanning calorimetry (DSC) and optical investigations. They were bond to be trigonal, space group P3̅, with the unit cell dimensions a = 7.699(1), c = 7.818(2) Å . The SiF2-6 anions, located in large cavities formed by hydrogen bonded cations, are strongly disordered at room temperature. The DSC measurements revealed a first-order phase transition at TC ≈ 177 K with a hysteresis of 4 K. The nature of the transition was confirmed by a sharp increase of the linear birefringence below TC. Optical observations under a polarizing microscope showed a domain structure of the low temperature phase, characteristic of ferroelastic materials

Parameterization of the coupling between strain and order parameter for LuF[SeO3]

2014 ◽  
Vol 47 (2) ◽  
pp. 701-711 ◽  
Author(s):  
Oxana V. Magdysyuk ◽  
Melanie Müller ◽  
Robert E. Dinnebier ◽  
Christian Lipp ◽  
Thomas Schleid
Keyword(s):  
Phase Transition ◽  
Order Parameter ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Time Resolved ◽  
Synchrotron Powder Diffraction ◽  
First Order Phase Transition ◽  
Temperature Phase Transition ◽  
First Order Phase

The high-temperature phase transition of LuF[SeO3] has been characterized by time-resolved high-resolution synchrotron powder diffraction. On heating, a second-order structural phase transition was found at 393 K, while on cooling the same phase transition occurs at 371 K, showing a large hysteresis typical for a first-order phase transition. Detailed analysis using sequential and parametric whole powder pattern fitting revealed that the coupling between the strain and the displacive order parameter determines the behaviour of the material during the phase transition. Different possible coupling mechanisms have been evaluated and the most probable rationalized.

Reversible phase transition of pyridinium-3-carboxylic acid perchlorate

2010 ◽  
Vol 66 (3) ◽  
pp. 387-395 ◽  
Author(s):  
Heng-Yun Ye ◽  
Li-Zhuang Chen ◽  
Ren-Gen Xiong
Keyword(s):  
Phase Transition ◽  
Carboxylic Acid ◽  
Relative Displacement ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Cell Parameters ◽  
Dsc Measurements ◽  
Reversible Phase Transition ◽  
Reversible Phase ◽  
Hydrogen Bonded

Pyridinium-3-carboxylic acid perchlorate was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurements show that this compound undergoes a reversible phase transition at ∼ 135 K with a wide hysteresis of 15 K. Dielectric measurements confirm the transition at ∼ 127 K. Measurement of the unit-cell parameters versus temperature shows that the values of the c axis and β angle change abruptly and remarkably at 129 (2) K, indicating that the system undergoes a first-order transition at T c = 129 K. The crystal structures determined at 103 and 298 K are all monoclinic in P21/c, showing that the phase transition is isosymmetric. The crystal contains one-dimensional hydrogen-bonded chains of the pyridinium-3-carboxylic acid cations, which are further linked to perchlorate anions by hydrogen bonds to form well separated infinite planar layers. The most distinct differences between the structures of the higher-temperature phase and the lower-temperature phase are the change of the distance between the adjacent pyridinium ring planes within the hydrogen-bonded chains and the relative displacement between the hydrogen-bonded layers. Structural analysis shows that the driving force of the transition is the reorientation of the pyridinium-3-carboxylic acid cations. The degree of order of the perchlorate anions may be a secondary order parameter.

scholarly journals 127I NQR and Crystal Structure Studies of [N(CH3)4]2 CdI4

2000 ◽  
Vol 55 (1-2) ◽  
pp. 225-229 ◽  
Author(s):  
Hideta Ishihara ◽  
Keizo Horiuchi ◽  
Thorsten M. Gesing ◽  
Shi-qi Dou ◽  
J.-Christian Buhl ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Order Phase Transition ◽  
Intensity Ratio ◽  
Room Temperature ◽  
Liquid Nitrogen Temperature ◽  
Temperature Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

The temperature dependence of 127I NQR and DSC as well as the crystal structure at room temperature of the title compound were determined. This compound shows a first-order phase transition of an order-disorder type at 245 K. Eight 127I(v1:m = ±1/2 ↔ ±3/2) NQR lines of 79.57, 81.86, 82.56, 83.36, 84.68, 87.72, 88.34, and 88.86 MHz, and corresponding eight 127I(v2: m = ±3/2 ↔±5/2) NQR lines were observed at liquid nitrogen temperature. Three 127I(υi) NQR lines wfth an intensity ratio of 1:1:2 in the order of decreasing frequency were observed just above the transition point and two NQR lines except for the middle-frequency line disappeared around room temperature. This temperature behavior of NQR lines is very similar to that observed in [N(CH3)4]2Hgl4. Another first-order phase transition takes place at 527 K. The structure of the room-temperature phase was redetermined: orthorhombic, Pnma, Z = 4, a = 1342.8(3), b = 975.7(2), c = 1696.5(3) pm. The NQR result of three lines with an intensity ratio of 1:1:2 is in agreement with this structure. The thermal displacement parameters of atoms in both cations and anions are large.

Synthesis, crystal structures and properties of the new compounds K7–x Ag1+x (XO4)4 (X = Mo, W)

2017 ◽  
Vol 73 (12) ◽  
pp. 1071-1077 ◽  
Author(s):  
Tatyana S. Spiridonova ◽  
Sergey F. Solodovnikov ◽  
Aleksandra A. Savina ◽  
Zoya A. Solodovnikova ◽  
Sergey Yu. Stefanovich ◽  
...  
Keyword(s):  
Second Harmonic ◽  
Analysis Data ◽  
Rietveld Analysis ◽  
Structure Type ◽  
Polar Space ◽  
Scanning Calorimetry ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
First Order Phase ◽  
New Compounds

Two new isostructural compounds, namely heptapotassium silver tetrakis(tetraoxomolybdate), K7–x Ag1+x (MoO4)4 (0 ≤ x ≤ 0.4), and heptapotassium silver tetrakis(tetraoxotungstate), K7–x Ag1+x (WO4)4 (0 ≤ x ≤ 0.4), have been synthesized and found to crystallize in the polar space group P63 mc (Z = 2) with the unit-cell dimensions a = 12.4188 (2) and c = 7.4338 (2) Å for K6.68Ag1.32(MoO4)4 (single-crystal data), and a = 12.4912 (5) and c = 7.4526 (3) Å for K7Ag(WO4)4 (Rietveld analysis data). Both structures represent a new structure type, with characteristic [K1(XO4)6] `pinwheels' of K1O6 octahedra and six XO4 tetrahedra (X = Mo, W) connected by common opposite faces into columns along the c axes. The octahedral columns are linked to each other through Ag1O4 tetrahedra along with the K2 and K3/Ag2 polyhedra, forming the polar rods (...Ag1O4–X1O4–empty octahedron–Ag1O4...). Ag1 is located almost at the centre of the largest face of its coordination tetrahedron and seems to have some mobility. The new structure type is related to the Ba6Nd2Al4O15 and CaBaSiO4 types, and to other structures of the α-K2SO4–glaserite family. The differential scanning calorimetry (DSC) and second harmonic generation (SHG) results show that both compounds undergo first-order phase transformations to high-temperature centrosymmetric phases.

High Temperature Phase Transitions in BiFeO3

2009 ◽  
Vol 1199 ◽  
Author(s):  
Donna Arnold ◽  
Christopher M Kavanagh ◽  
Philip Lightfoot ◽  
Finlay Doogan Morrison
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Order Phase Transition ◽  
Structure Type ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
First Order ◽  
Β Phase ◽  
First Order Phase Transition ◽  
First Order Phase

AbstractThe high temperature phases of BiFeO3 have courted much controversy with many conflicting structural models reported, in particular for the paraelectric β-phase. High temperature powder neutron diffraction (PND) experiments indicate that the ferroelectric (R3c) α-phase transforms to the paraelectric β-phase at approximately 820 °C via a first order phase transition. We demonstrate that this phase is unambiguously orthorhombic, adopting the GdFeO3 structure-type with a space group Pbnm. On further heating BiFeO3 undergoes another first order phase transition (β-γ) at approximately 930 °C which is marked by a discontinuous decrease in cell volume consistent with an insulator-metal transition. Close inspection of the PND data show no evidence of any symmetry change, with the postulated γ-phase remaining orthorhombic Pbnm. In addition we present PND and impedance spectroscopy data for BiFeO3 which suggest that the so-called ‘Połomska’ transition observed by some authors at approximately 185 °C is not intrinsic.

Structural and magnetic properties on F-doped LiVO2 with two-dimensional triangular lattice

2011 ◽  
Vol 1344 ◽  
Author(s):  
Yang Li ◽  
Xiaoxiang Li ◽  
Lihua Liu ◽  
Ning Chen ◽  
Jose García ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Thermal Hysteresis ◽  
Magnetic Ordering ◽  
Lattice Parameter ◽  
Two Dimensional ◽  
Scanning Calorimetry ◽  
Heat Measurement ◽  
Dsc Measurements ◽  
First Order Phase Transition

ABSTRACTThe layered oxide LiVO2 recently has received more attention due to its interesting structural and magnetic behaviors involving the two-dimensional magnetic frustration in these systems. We synthesized a series of F-doped LiVO2 samples, and reported the F-doping effect on the structure and transition temperature Tt. The samples LiVO2-xFx (x=0, 0.1, 0.2 and 0.3) were characterized by X-ray diffraction, scanning electron microscope (SEM), differential scanning calorimetry (DSC), magnetic susceptibility and specific heat measurement. The structural analysis shows that with increasing x, the ratio of lattice parameter c/a increasing, i.e. in the a-b plane the lattice is compressed while in the c-axis direction the lattice expands. The DSC measurements show that a first-order phase transition happens at around 500 K, and the thermal hysteresis around phase transition temperature Tt increases with increasing x. Substitution of O with F ions results in a change of two dimensional characteristics and the distortion of the VO6 block in structure, which significantly influence the magnetic ordering transition temperature Tt.

Chlorine-35 NQR Study of a Structural Phase Transition in (ND4)2PdCl6

1998 ◽  
Vol 53 (6-7) ◽  
pp. 514-517 ◽  
Author(s):  
Yoshio Kume ◽  
Tetsuo Asaji
Keyword(s):  
Phase Transition ◽  
Structural Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
First Order Phase Transition ◽  
Temperature Dependences ◽  
First Order Phase

Abstract Temperature dependences of 35Cl NQR frequencies and spin-lattice relaxation times were measured at 4.2 to 400 K for natural and deuterated ammonium hexachloropalladate. It was confirmed that only the deuterated salt undergoes a first order phase transition at 30 K. The crystal structure of the low-temperature phase is predicted to be the same as that of the deuterated ammonium hexachloroplatinate and hexachloroplumbate. The mechanism of the deuteration-induced phase transition is discussed.

Synthesis and Lattice Distortion of Ferroelectric/Antiferroelectric Bi(III)-containing Perovskites

2002 ◽  
Vol 755 ◽  
Author(s):  
Yoshiyuki Inaguma ◽  
Atsushi Miyaguchi ◽  
Tetsuhiro Katsumata
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Order Phase Transition ◽  
Lattice Distortion ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
Lattice Distortions ◽  
First Order Phase

ABSTRACTBi(III)-containing perovskites Bi1/2Ag1/2TiO3 and Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni) were synthesized under oxygen pressure as high as approximately 1 MPa and under a pressure as high as 6 GPa, and the lattice distortions were investigated. It was found that ferroelectric Bi1/2Ag1/2TiO3 may be rhombohedrally distorted. In constrast, Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni), the structure of which is different from GdFeO3-type compound, is monoclinically distorted. The ratio of lattice parameters of the monoclinic perovskite-subcell for Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni), am/bm is larger than that of GdFeO3-type perovskites, though the tolerance factor is close. In addition, it was found that Bi(Ni1/2Ti1/2)O3 undergoes a first-order phase transition from a GdFeO3-type phase(high-temperature phase) at around 490 K. These results indicate that the Bi3+ character in Bi(III)-containing perovskites strongly influences the structure distortion.

In Situ Measurement of Phase Transition of Layered Perovskite BaLn2Mn2O7

2010 ◽  
Vol 67 ◽  
pp. 113-117 ◽  
Author(s):  
Hiromi Nakano ◽  
Nobuo Ishizawa ◽  
Hirohisa Sato ◽  
Naoki Kamegashira
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Order Phase Transition ◽  
High Temperature Phase ◽  
Layered Perovskite ◽  
Temperature Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

The BaLn2Mn2O7 (Ln = rare earth) has a Sr3Ti2O7-type structure with double block oxygen octahedra belonging to the Ruddlesden-Popper-Type homologous series AO(ABO3)2. In-situ measurement of the phase transition for BaLn2Mn2O7 was performed using single-crystal X-ray diffraction and a high-temperature transmission electron microscope (TEM). Two types of transitions were observed in BaPr2Mn2O7: the transition from primitive tetragonal (P42/mnm) to body-centered tetragonal (I4/mmm) at around 400 K and the first-order phase transition at around 1040 K. Multiple phase transitions were also observed in BaEu2Mn2O7, with one from P42/mnm to I4/mmm at around 400 K and another, above 550 K, as a first-order phase transition. The high-temperature phase had a 1.5% lattice mismatch along the c-axis compared with the low-temperature phase. We succeeded in recording for the first time in-situ structural change in BaGd2Mn2O7 as a movie by high-temperature TEM. The high-temperature phase nucleated parallel to the (00l) plane as a layer above 550 K and grew until covering the entire inspected region at around 1023 K. The first-order phase transition was caused by the structural and/or electrical distortion of the layered perovskite structure composed of Jahn-Teller ion Mn3+.

scholarly journals Components Influence On Dielectric Properties Of Ferroelectric Composite Materials

2016 ◽  
Vol 1 (1) ◽  
pp. 51
Author(s):  
O.V. Efimova ◽  
E.V. Stukova ◽  
E.Yu. Koroleva
Keyword(s):  
Phase Transition ◽  
Dielectric Properties ◽  
Ferroelectric Phase ◽  
Volume Fraction ◽  
Temperature Phase ◽  
Cooling Mode ◽  
First Order ◽  
First Order Phase Transition ◽  
Temperature Phase Transition ◽  
First Order Phase

<p>The dielectric properties of ferroelectric composite (NH<sub>4</sub>HSO<sub>4</sub>)<em><sub>x</sub></em>/(PbTiO<sub>3</sub>)<em><sub>1-x</sub></em> is studied for x ranging from 0,00 to 0,50. Measurements of permittivity were performed by heating-cooling mode temperature range from 130 K to 380 K. The value of the temperature interval of existence of the ferroelectric phase increases by ~5 degrees and independent at the volume fraction of particulate inclusions in composites. It is shown that the inclusion of PbTiO<sub>3</sub> particles gives rise to hysteresis upper temperature phase transition, which may indicate a change in the type of phase transition of the second order on the first-order phase transition.</p>

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