THE HIGH TEMPERATURE RESISTIVITY OF Ba2YCu3O7−x

1988 ◽  
Vol 01 (09n10) ◽  
pp. 389-392 ◽  
Author(s):  
ZHANG XINGKUI ◽  
ZHU SHINING ◽  
WANG HAO ◽  
ZHANG SHIYUAN ◽  
YE SU ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Oxygen Evolution ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Drude Model ◽  
Temperature Resistivity ◽  
Derivative Thermogravimetry ◽  
Tetragonal Phase Transition

The high temperature resistivity (ρ), thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used to characterize superconductor Ba2YCu3O7−x (BYCO) in O2, air and N2. The resistivity is linear from room temperature to 350°C and then deviate from linearity with oxygen evolution, the derivative of resistivity dρ/dT increases abruptly near orthorhombic to tetragonal phase transition. These phenomena can give good explanations for a two-band Drude model.

STRUCTURAL CHANGES OF Ni-DOPED YBCO AT DIFFERENT TEMPERATURE

2005 ◽  
Vol 19 (01n03) ◽  
pp. 319-322
Author(s):  
L. ZHANG ◽  
H. L. DU ◽  
X. F. RUI ◽  
X. F. SUN ◽  
H. ZHANG
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Structural Changes ◽  
Close Correlation ◽  
Bond Lengths ◽  
Ni Content ◽  
The Difference ◽  
Tetragonal Phase Transition

In YBa 2 Cu 3-x Ni x O y at about 480°C all the samples show a tetragonal phase. Comparing the structural changes at 480°C with those at room temperature, the bond lengths such as Cu (1)- O (4) and Cu (2)- O (4) vary regularly with Ni -content increasing at room temperature, but not at high temperature. It suggests that there is a close correlation between structural changes and superconductivity in this system. The difference of orthorhombic- tetragonal phase -transition is also discussed between undoped YBCO and Ni -doped YBCO at high temperature.

High-temperature X-ray powder diffraction study of the tetragonal-cubic phase transition in nanocrystalline, compositionally homogeneous ZrO2–CeO2 solid solutions

2008 ◽  
Vol 23 (S1) ◽  
pp. S70-S74 ◽  
Author(s):  
L. M. Acuña ◽  
R. O. Fuentes ◽  
D. G. Lamas ◽  
I. O. Fábregas ◽  
N. E. Walsöe de Reca ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Solid Solutions ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Cubic Phase ◽  
X Ray ◽  
First Order

Crystal structure of compositionally homogeneous, nanocrystalline ZrO2–CeO2 solutions was investigated by X-ray powder diffraction as a function of temperature for compositions between 50 and 65 mol % CeO2. ZrO2-50 and 60 mol % CeO2 solid solutions, which exhibit the t′-form of the tetragonal phase at room temperature, transform into the cubic phase in two steps: t′-to-t″ followed by t″-to-cubic. But the ZrO2-65 mol % CeO2, which exhibits the t″-form, transforms directly to the cubic phase. The results suggest that t′-to-t″ transition is of first order, but t″-to-cubic seems to be of second order.

ORTHORHOMBIC-TO-TETRAGONAL PHASE TRANSITION IN 6.8-nmPbTiO3 NANOPARTICLES

2005 ◽  
Vol 19 (15n17) ◽  
pp. 2669-2675
Author(s):  
Y. DENG ◽  
M. S. ZHANG ◽  
J. L. WANG ◽  
Q. R. GU
Keyword(s):  
Phase Transition ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Pt Nanoparticles ◽  
Orthorhombic Phase ◽  
Lattice Parameter ◽  
Continuous Change ◽  
Grain Sizes ◽  
Tetragonal Phase Transition ◽  
Second Order Phase Transition

Crystalline 6.8-nm PbTiO 3 (PT) nanoparticles were prepared through a modified solgel method. The samples showed high homogeneity and in orthorhombic phase. We examined the structural and phonon characteristics in PT nanoparticles with various grain sizes, finding that the orthorhombic phase begins to emerge at room temperature when particle size reduces to 11 nm. In the 6.8-nm PT nanoparticles, an orthorhombic-to-tetragonal phase transition at 190°C was detected by recording the Raman spectra as a function of temperature. The thermal properties of PT nanocrystals were also studied, demonstrating that the orthorhombic-to-tetragonal phase transition in the 6.8-nm PT nanoparticles is a second-order phase transition with continuous change in lattice parameter.

High-Temperature Synchrotron X-Ray Powder Diffraction Study of the Orthorhombic–Tetragonal Phase Transition in La0.63(Ti0.92,Nb0.08)O3

2002 ◽  
Vol 164 (1) ◽  
pp. 51-59 ◽  
Author(s):  
Roushown Ali ◽  
Masatomo Yashima ◽  
Masahiko Tanaka ◽  
Hideki Yoshioka ◽  
Takeharu Mori ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Diffraction Study ◽  
Powder Diffraction ◽  
Tetragonal Phase ◽  
X Ray ◽  
Tetragonal Phase Transition

Room-Temperatrue Structure and Geometrical Analysis of the Cubic–Tetragonal Phase Transition in Dodecasil 3C-THF

1997 ◽  
Vol 53 (1) ◽  
pp. 18-24 ◽  
Author(s):  
K. Knorr ◽  
W. Depmeier
Keyword(s):  
Phase Transition ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Group Symmetry ◽  
Ambient Conditions ◽  
Space Group ◽  
Symmetry Properties ◽  
Ideal Framework ◽  
Tetragonal Phase Transition ◽  
The Ideal

The structure of dodecasil 3C-tetrahydrofuran [Si68O136]·4M, M = (CH2)4O, at room temperature was determined from a merohedrally twinned crystal in the tetragonal space group I41/a. The deformation of the ideal framework at the cubic tetragonal phase transition at T c ≃ 365 K could be explained mainly by two different symmetry-breaking processes. (i) A tetragonal tetrahedron distortion of the Si(5) tetrahedra and (ii) a hitherto unknown local one-dimensional tilt mechanism, localized in the tetrahedral network. The location of the axes of this tilt system coincides with the positions of the fourfold inversion axes in the space group I41/a. At room temperature the tilt angle is = 24°. The symmetry properties of the tilt system can explain the reduction of space-group symmetry from the space group of the ideal structure Fd\overline 3m to the space group at ambient conditions I41/a. The guest molecule tetrahydrofuran does not fit the cage symmetry and has been found to be dynamically disordered. The average structure shows an off-center location in the [51264] cage and follows the local \overline 4symmetry of the cage.

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