scholarly journals Low-temperature phase transition and highpressure phase stability of 1H-pyrazole-1carboxamidine nitrate

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Piotr Rejnhardt ◽  
Marek Drozd ◽  
Marek Daszkiewicz
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase I ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Negative Thermal Expansion ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Scanning Calorimetry

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.

Characterization of the pressure-induced second-order phase transition in the mixed-valence vanadate BaV6O11

2009 ◽  
Vol 65 (3) ◽  
pp. 326-333 ◽  
Author(s):  
Karen Friese ◽  
Yasushi Kanke ◽  
Andrzej Grzechnik
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Mixed Valence ◽  
Volume Effect ◽  
Unit Cell ◽  
Additional Degree ◽  
Diamond Anvil

The pressure dependence of the structure of the mixed-valence vanadate BaV6O11 was studied with single-crystal X-ray diffraction in a diamond–anvil cell. The compressibility data could be fitted with a Murnaghan equation of state with the zero-pressure bulk modulus B 0 = 161 (7) GPa and the unit-cell volume at ambient pressure = 387.1 (3) Å^3 (B′ = 4.00). A phase transition involving a symmetry reduction from P63/mmc to P63 mc can be reliably detected in the high-pressure data. The estimated transition pressure lies in the range 1.18 < P c < 3.09 GPa. The transition leads to a breaking of the regular Kagomé net formed by part of the V ions. While in the ambient pressure structure all V—V distances in the Kagomé net are equal, they split into inter-trimer and intra-trimer distances in the high-pressure phase. In general, these changes are comparable to those observed in the corresponding low-temperature transition. However, the pressure-induced transition takes place at a lower unit-cell volume compared with the temperature-induced transition. Furthermore, overall trends for inter-trimer and intra-trimer V—V distances as a function of the unit-cell volume are clearly different for datapoints obtained by variation of pressure and temperature. The behavior of BaV6O11 is compared with that of NaV6O11. While in the latter compound the transition can be explained as a pure volume effect, in BaV6O11 an additional degree of freedom related to the valence distribution among the symmetrically independent vanadium sites has to be taken into account.

Valence Crossover of Ce Ions in CeCu2Si2 under High Pressure –Pressure Dependence of the Unit Cell Volume and the NQR Frequency–

2013 ◽  
Vol 82 (11) ◽  
pp. 114701 ◽  
Author(s):  
Tatsuo C. Kobayashi ◽  
Kenji Fujiwara ◽  
Keiki Takeda ◽  
Hisatomo Harima ◽  
Yoichi Ikeda ◽  
...  
Keyword(s):  
High Pressure ◽  
Cell Volume ◽  
Pressure Dependence ◽  
Unit Cell Volume ◽  
Unit Cell

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.

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.

Enantiotropic phase transition in a binuclear tin complex with anO,N,O′-tridentate ligand

2013 ◽  
Vol 69 (11) ◽  
pp. 1336-1339 ◽  
Author(s):  
Anke Schwarzer ◽  
Lydia E. H. Paul ◽  
Uwe Böhme
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Tridentate Ligand ◽  
Asymmetric Unit ◽  
Disorder Transition ◽  
Vinyl Group

The crystal structure of chlorido{μ-2-[(2-oxidobenzylidene)amino]ethanolato-κ4O,N,O′:O′}{2-[(2-oxidobenzylidene)amino]ethanolato-κ3O,N,O′}trivinylditin(IV), [Sn2(C2H3)3(C9H9NO2)2Cl], is disordered above 178 K. A doubling of the unit-cell volume is observed on cooling. The asymmetric unit at 93 K contains two ordered molecules. The phase transition corresponds to an order–disorder transition of one vinyl group bound to the SnIVatom.

scholarly journals Geometric considerations of the monoclinic–rutile structural transition in VO2

2019 ◽  
Vol 48 (25) ◽  
pp. 9260-9265
Author(s):  
Shian Guan ◽  
Aline Rougier ◽  
Matthew R. Suchomel ◽  
Nicolas Penin ◽  
Kadiali Bodiang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Structural Transition ◽  
Unit Cell

Geometrical and experimental examinations of VO2 show how hysteretic phase transition phenomena across the MIT can be driven by positive crystal energy effects of increasing unit cell volume.

FexCu1-xBa2YCu2O7+y SUPERCONDUCTORS SYNTHESIZED BY HIGH PRESSURE

2005 ◽  
Vol 19 (01n03) ◽  
pp. 221-223 ◽  
Author(s):  
Y. H. LIU ◽  
G. C. CHE ◽  
K. Q. LI ◽  
Z. X. ZHAO ◽  
Z. Q. KOU ◽  
...  
Keyword(s):  
High Pressure ◽  
Cell Volume ◽  
Oxygen Content ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Lattice Parameter ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxygen Coordination

Systematic studies of x-ray diffraction(XRD), superconductivity and Mössbauer effect on Fe x Cu 1-x Ba 2 YCu 2 O 7+y ( x =0.00~0.70) superconductors synthesized by high pressure (HP) were summarized. All the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples (synthesized by ambient pressure). The HP-samples have higher oxygen content than the AM-samples. Moreover, for the HP-sample with x =0.5, all of the Fe located in the CuO x chains have fivefold-oxygen coordination.

Growth, Structural and High Pressure Study of GeS0.25Se0.75 and GeS0.75Se0.25 Single Crystals

2013 ◽  
Vol 665 ◽  
pp. 37-42
Author(s):  
G.K. Solanki ◽  
Dipika B. Patel ◽  
Sandip Unadkat ◽  
N.N. Gosai ◽  
Yunus Gafur Mansur
Keyword(s):  
High Pressure ◽  
Cell Volume ◽  
Single Crystals ◽  
Unit Cell Volume ◽  
Structural Changes ◽  
Unit Cell ◽  
Lattice Parameters ◽  
X Ray ◽  
Ray Density ◽  
High Pressure Study

The orthorhombic semi-conducting compound GeS0.25Se0.75 and GeS0.75Se0.25 possess interesting electrical properties and can been the subject of numerous investigations. The changes in solids under high pressure can reveal several new features of interatomic forces, which are responsible for their diverse physical properties. Authors have carried out growth of GeS0.25Se0.75 and GeS0.75Se0.25 crystals by Direct Vapor Transport (DVT) technique. For compositional confirmation energy dispersive analysis of X-ray (EDAX) has been used. EDAX results show that the grown crystals are nearly stoichiometrycally perfect. The grown crystals have been characterized by X-ray diffraction technique (using Philips X Pert MPD diffractometer) for structural characterization. These crystals are crystallized in orthorhombic structure. The values of lattice parameters, unit cell volume and X-ray density are calculated and presented. It is observed from lattice parameters, unit cell volume and X-ray density, that as the content of sulfur increases the value of all the lattice parameters decreases. High pressure study is also of great importance to visualize the mechanism governing the structural changes and to reveal solid state properties associated with different structure. For the room temperature measurement of resistance as a function of pressure, up to 7 GPa, the sample was set at the centre of the talc disc on the lower anvil. The pressure was generated by a hydraulic press on the Bridgman type tungsten carbide opposed anvil apparatus with in-situ Bismuth pressure calibration. The resistance was measured in several independent runs on these crystals as a function of pressure and was found to be reproducible. The results of variation of electrical resistance do not show presence of any phase transition up to 7 GPa. We investigate in GeS0.25Se0.75 and GeS0.75Se0.25 single crystals that as sulfur content increases, resistance of this compound increases.

scholarly journals Negative thermal expansion in YbMn2Ge2 induced by the dual effect of magnetism and valence transition

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Yongqiang Qiao ◽  
Yuzhu Song ◽  
Andrea Sanson ◽  
Longlong Fan ◽  
Qiang Sun ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Intermetallic Compound ◽  
Cell Volume ◽  
Valence State ◽  
Unit Cell Volume ◽  
Negative Thermal Expansion ◽  
Combined Effect ◽  
Dual Effect ◽  
Valence Transition ◽  
Magnetovolume Effect

AbstractNegative thermal expansion (NTE) is an intriguing property, which is generally triggered by a single NTE mechanism. In this work, an enhanced NTE (αv = −32.9 × 10−6 K−1, ΔT = 175 K) is achieved in YbMn2Ge2 intermetallic compound to be caused by a dual effect of magnetism and valence transition. In YbMn2Ge2, the Mn sublattice that forms the antiferromagnetic structure induces the magnetovolume effect, which contributes to the NTE below the Néel temperature (525 K). Concomitantly, the valence state of Yb increases from 2.40 to 2.82 in the temperature range of 300–700 K, which simultaneously causes the contraction of the unit cell volume due to smaller volume of Yb3+ than that of Yb2+. As a result, such combined effect gives rise to an enhanced NTE. The present study not only sheds light on the peculiar NTE mechanism of YbMn2Ge2, but also indicates the dual effect as a possible promising method to produce enhanced NTE materials.

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