The Influences of Cool- and Hot-Pressure Treatment on the Phase Transition and Superconductivity of YBa2Cu3O7-
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摘要: 本文研究了冷压(2.2~5.2 GPa)与热压(2.2 GPa,2.50~950 ℃)对YBa2Cu3O7-的正交四方相转变区和超导电性的影响。冷压保持其正交结构,但破坏了超导性,在98 K(失超点)到室温呈半导体特性,再在空气中烧结,可恢复液氮温区的零电阻状态。以Cu锅密封样品,热压处理至950 ℃,不发生Cu的析出。热压处理后,98 K(失超点)到室温呈半导体特性,再经通氧烧结,于86 K出现零电阻。热压处理过程,从450~950 ℃为正交四方转变区。950 ℃为转变结束温度,大大高于氧气、空气、氮气、真空状态的温度。400 ℃附近为起始转变温度,低于氮气、氧气气氛的温度。因此相变区加宽。T0-t结束温度升高,与Cu锅的抑制还原作用有密切关系。如降低高压淬火速率(102 ℃/s),或随后辅以氧气氛中的后处理,将有利于获得既有高密度又有高Tc的YBa2Cu3O7-超导体。Abstract: In this paper, the influence of cool- and hot-pressure treatment were studied on the phase transition region from or thorhombic to tetragonal and superconductivity in YBa2Cu3O7-. After the cool pressure treatment of 2.2~5.2 GPa, the samples remained the orthorhombic structure, but lost their superconductivities and kept up the semiconductivity in the region from 98 K to room temperature. If the samples are sintered in air, their zero resistance states will be regained. When the samples were sealed hermetically into a Cu bowl, there was no separation of Cu in the samples within the region of hot-pressure temperature from 250 ℃ up to 950 ℃. After the hot-pressure treatment (2.2 GPa, 250~950 ℃), the samples were in semiconductiviting state in the region of 98 K to room temperature. If the samples are followed by an after-treatment in oxygen, the zero resistance state can be observed (at about 86 K). In the process of hot-pressure treatment, it was found that the transition region of orthorhombic to tetragonal is in the 450~950 ℃, 950 ℃ is the end temperature of transition, which is higher than that of samples obtained by sintering in oxygen, air, nitrogen and vacuum. And about 400 ℃ is the onset temperature of transition, which is lower than that in nitrogen, air and oxygen. Therefore the phase transition region is widened, and the end temperature of T0-t raises. These are related to that the Cu bowl restrains the reduction role under high pressure. If the quenching rate under high pressure is slowed (102 ℃/s), or the samples are followed by an after-treatment in O2, the YBa2Cu3O7- both with high density and Tc can be obtained. The deficiency and hole of oxygen are also discussed here.
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