Compatible phases of the Y₂O₃–CuO–Cu₂O system in air

Abstract

The phase diagram of the Y 2 O 3 -CuO-Cu 2 O system was constructed as a function of temperature in air by means of thermal analysis and x-ray diffraction. The phase Y 2 Cu 2 O 5 was found to be stoichiometric and melted peritectically at about 1110 °C. A new intermediate phase with the composition YCu 2 O 25 was discovered. It exists between 990 and 1105 °C in air and quenching did not preserve it to room temperature. High temperature x-ray diffraction established its pattern and confirmed its peritectic decomposition. Above 1110 C C YCu 2 O 25 consists of Y 2 O 3 and liquid. The results of this system are shown on a ternary system as well as on a pseudo-binary phase diagram. The solid state reactions were established. Melting occurs with isothermal oxygen loss or gain, depending on the initial composition.

Phase diagrams for the YBa2Cu3O7 family — ANNO 1996

“…20. One additional phase with suggested composition YCu202.5 is seen [215] between some 1000-1100~ by high-temperature PXD. This phase could not be quenched to room temperature.…”

“…The crystal structure [210][211][212][213][214] contains slightly deformed Cu--O coordination tetrahedra, and the oxygen content is therefore structurally fixed. The x-t phase diagram for the Y(O)--Cu(O) system in air, as obtained [204,215] by DTA and PXD, is shown in Fig. 18.…”

“…The Y2CuzO5 phase is entropy stabilized [204,216] and therefore unstable at low temperatures. A mixture of the binary oxides is more stable below 680~ [175], referring to ambient partial pressures of [204,215] oxygen (730~ determined [217] from a change in decomposition products of more complex oxides, whereas 700~ is calculated from thermodynamic data [207]). m-RE2Cu2Os, has been observed [218][219][220] in an extremely narrow region of temperatures just above 1000*C for large trivalent RE=Nd and La.…”

Analysis of reactions during sintering of CuO-doped 3Y-TZP nano-powder composites

“…These endothermic and exothermic signals can be ascribed to respectively melting and solidification of Y 2 Cu 2 O 5 as was also observed in the same temperature region by Mayo et al 10 and Gadalla and Kongkachuichay. 17 The formation of Y 2 Cu 2 O 5 in our system will be discussed in Section 4 of this paper.…”

“…17 In ZrO 2 -Y 2 O 3 solid solutions Y tends to segregate to the grain boundaries at elevated temperatures (≥800 • C). 18 It was proposed in literature that a reaction takes place between CuO and yttria as segregated to the 3Y-TZP grain boundaries, to form an yttria-copper-oxide phase during sintering 9-11 of CuO-doped 3Y-TZP systems.…”