Premium
The thermodynamic equilibrium of the formation process of High‐ T c superconducting phase YBa 2 Cu 3 O 7−x
Author(s) -
Huan Le Van,
Tuong Le Thi Cat
Publication year - 1990
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170251003
Subject(s) - superconductivity , gibbs free energy , chemistry , thermodynamics , phase (matter) , diffusion , oxygen , activation energy , analytical chemistry (journal) , physics , condensed matter physics , organic chemistry , chromatography
Analysing the equilibrium state of the formation reaction of the high‐ T c superconducting phase 1:2:3 (YBa 2 Cu 3 O 7−x ) on the base of the pressure‐temperature‐oxygen content ( P ‐ T − x ) correlation research and using the Van't‐Hoff equation, the Gibbs free energy (Δ G m ) of the reaction has been calculated for the first time. It is seen that the absolute value of Δ G m is not large and of the order of 2.5 kcal · mole −1 . This leads to an instability of the 1:2:3 phase. Also, from the calculated values of Δ G m relative stability regions of the 1:2:3 phase are determined for different values of x. Combinatively analysing the relation lg P o 2= A − B / T (where A – the x‐dependent constant, and value of B was determined to be equal to 10518 atm. K) and the value of ΔG m , we come to the conclusion that the synthesis of YBa 2 Cu 3 O 7 − x when x → 0 must be carried out under high oxygen pressure and low temperature for a lasting time, because the reaction rate is limited by slow diffusion in the solid phase.