Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

First Advisor

D. C. Johnston

Abstract

La[subscript] 2-xSr[subscript] xCuO[subscript]4 (0 ≤ x ≤ 0.15) can all be intercalated with oxygen by an novel electrochemical oxidation method. Bulk superconductivity is found with an onset T[subscript] c ≈ 40 K for the whole range 0.01 ≤ x ≤ 0.15; for x = 0.25 and 0.33, the electrochemical oxidation did not improve the superconducting properties. The magnetic susceptibility [chi](T = 50-320 K) data for La[subscript]2CuO[subscript]4.11 and La[subscript]1.92Sr[subscript]0.08CuO[subscript]4.07 are nearly identical with those of conventionally prepared La[subscript]1.85Sr[subscript]0.15CuO[subscript]4, indicating that the hole doping level (p) in the CuO[subscript]2 planes of the three compounds is nearly the same. Combined thermogravimetric analysis and iodometric titration experiments indicate that part of the intercalated oxygen has a formal valence close to -1. The maximum doped-hole concentration in the CuO[subscript]2 planes that can be achieved from combined Sr-doping and electrochemical oxygen doping for 0 ≤ x ≤ 0.15 is p ≈ 0.16 holes/formula unit;Oxygen can also intercalate into single crystal La[subscript]2CuO[subscript]4 through a slow electrochemical oxidation process. The required low current and long time for the charging process reflects that the oxygen intercalation for a single crystal is limited by its small specific surface area and long diffusion distance. The anisotropic superconducting, magnetic and transport properties are summarized and compared with those of polycrystalline La[subscript]2CuO[subscript]4+[delta] as well as of YBa[subscript]2Cu[subscript]3O[subscript]7-[delta] and La[subscript] 2-xSr[subscript] xCuO[subscript]4 single crystals. The single crystal La[subscript]2CuO[subscript]4+[delta] has a maximum T[subscript] c ≈ 40 K, which is lower than that (T[subscript] c ≈ 42-45) of the corresponding polycrystalline samples;The magnetic phase diagram of La[subscript] 2-xSr[subscript] xCuO[subscript]4 in the antiferromagnetic (AF) regime (0 ≤ x ≤ 0.02) has been derived from [superscript]139La NQR studies from 4 to 250 K. The data demonstrate localization of the doped holes' charge below ~30 K, followed by freezing of the holes' effective spin degrees of freedom below T[subscript] f ≈ (815 x) K into a spin-glass-like (SG) state which is superimposed on the AF background. These and previous results allow a detailed magnetic phase diagram to be constructed for x ≤ 0.05 and reveal a distinct cross-over at x ≈ 0.02 in the nature of the SG transition.

DOI

https://doi.org/10.31274/rtd-180813-12483

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Fangcheng Chou

Language

en

Proquest ID

AAI9335049

File Format

application/pdf

File Size

154 pages

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