HIGH-PRESSURE SYNTHESIS OF SR2CUO2-CL2-DELTA' COMPOUNDS(DELTA)

We synthesized K2NiF4-type Sr2CuO2+deltaCl2-delta' compounds with oxyg en, partially substituted for the apical chlorine sites, by using high -pressure technique. As compared with the ambient pressure phase Sr2Cu O2Cl2, a decrease in the chlorine content and an increase in the oxyge n content were confirmed by energy dispersive X-ray analyzer attached to a scanning electron microscope (SEM-EDX) analysis and iodometric ti tration. As the substitution content of oxygen for chlorine increased, the crystal lattice shrank gradually and the average Cu valence incre ased to about + 2.5. Moreover, the magnitude of the electrical resisti vity decreased monotonically, which is consistent with the increase in the hole content. However, the absence of superconductivity and the r elatively large positive thermoelectric power suggest that there are s till insufficient mobile holes in the CuO2 plane of these compounds. ( C) 1998 Elsevier Science B.V. All rights reserved.