Influence of low-temperature fluorination process on the characteristics of superconductors YBa2Cu3O7−δ and Bi4(Ca, Sr)6Cu4O16+δ

Electrochemical Fluorination of La2CuO4: A Mild “Chimie Douce” Route to Superconducting Oxyfluoride Materials

“…Another process is fluorination by solid−gas reactions, which are generally performed at temperatures around 300 °C using a fluorinated gas such as NF 3 , or F 2 . ,, Such a fluorination has attracted considerable attention as a technique to introduce carriers for inducing superconductivity, resulting in drastic changes in structures and superconducting properties. , However, great care is required in handling the toxic F 2 gas . To solve this problem, fluorination by ionic bombardment with a fluoride beam has been developed. , …”

High-temperature superconductors based on complex layered copper oxyfluorides

“…17,18 However, the Sr 2 CuO 2 F 2+d compound can be synthesised under much milder conditions (compared to those required for the solid-phase reaction) by treating Sr 2 CuO 3 with a gaseous mixture of F 2 (10%) and N 2 (90%) at 483 K for 15 min, 19 with NH 4 F in the presence of oxygen at 498 K for 6 ± 8 h, 18,20,21 or with XeF 2 at 433 ± 623 K (from 40 min to 10 h). 17 Low-temperature fluorination afforded fluorine derivatives of layered cuprates, viz., YBa 2 Cu 3 O 6+d , 22,23 La 2 CuO 4 , 24 M 27x A 1+x Cu 2 O 67d (M = La or Nd; A = Ca or Sr), 25 Pb 2 Sr 2 YCu 3 O 8 , 26 etc. Fluorine derivatives of complex cuprates decompose upon heating to form thermodynamically stable products.…”

“…3. Fluorinating agents for the synthesis of fluorine-containing high-temperature superconductors Low-temperature syntheses of complex copper oxyfluorides were carried out with the use of various fluorinating agents, viz., gaseous fluorine (pure 22,27 or in mixtures with other gases 19,24 ), NF 3 , 23 NH 4 F, 28 ± 31 NH 4 HF 2 , 32,33 transition-metal fluorides (ZnF 2 , CuF 2 , NiF 2 , AgF 2 ) 34 ± 38 and ClF 3 . 39,40 Xenon difluoride, which offers promise as a fluorinating agent, was first proposed for fluorination of HTSC cuprates in the study.…”

“…In most cases, fluorination of the strongly oxidised YBa 2 Cu 3 O 6+d phase with d nearly-unity allows one to prepare compounds possessing T c no higher than that achieved for the optimally oxygen-doped sample. 22,23,53,54 However, it was reported that the treatment of YBa 2 Cu 3 O 6+d with a mixture of nitrogen and fluorine led to an increase of T c from 92 to 96 K. 55 An increase in the degree of fluorination of the starting phase Y123 gave rise to a fluorinated phase with a tetragonal unit cell regardless of the hyperstoichiometric oxygen content. 53,56 Fluorination, like the oxygen incorporation, was accompanied by the contraction of the structure along the c axis.…”

Preparation, Thermal Behaviour, and Structure of Calcium Trifluoroacetate Monohydrate

“…In this case, the pyrolysis results in the formation of ®lms with a rather broad transition to the superconducting state due to the reactivity of the intermediate alkaline earth oxides participating in the composition of all hightemperature oxide superconductors and to carbon contamination during the decomposition of these carboxylates. On the other hand, it has been shown that uorine gas treatment prevents atmospheric degradation and improves the properties of oxide superconductors [20]. On this basis it can be assumed that better pyrolytic ®lms might be obtained from precursors yielding the corresponding metal¯uorides upon decomposition.…”