Effective Oxygen Content and Properties of La0.74Ca0.26MnO3+das a Function of Synthesis Conditions

✍ Scribed by B. Dabrowski; P.W. Klamut; Z. Bukowski; R. Dybzinski; J.E. Siewenie

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 189 KB
• Volume: 144
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8210

✦ Synopsis

Using the thermogravimetric analysis measurements the e4ective oxygen content was measured for La 0.74 Ca 0.26 MnO 3 ؉ d samples synthesized at high oxygen pressure. All samples were single-phase with orthorhombic, Pbnm, structure for the entire range of e4ective oxygen contents achieved, 04 43 ؉ d4 43.066. The unit-cell volume decreases with increasing d, con5rming that the holes are doped uniformly. The magnitoresistive transition temperatures increase intially with increasing e4ective oxygen contents but decrease for larger amounts of d' '0.008. Magnetic moment per Mn decreases with increasing d in agreement with the hole doping given by h ‫؍‬ x ؉ 2d. Structural and physical properties are consistent with the defect model of vacancies on the (La, Ca) and Mn sites in equal number, *& &d/(3 ؉ d). Results indicate that a small vacancy concentration on metal sites, *( (0.003, does not produce major structural or electronic e4ects other than the e4ective hole doping that increases T . For larger vacancy concentrations, scattering on defects may be a cause of observed decrease and broadening of T .