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

摘要: Using the thermogravimetric analysis measurements effective oxygen content was measured for La0.74Ca0.26MnO3+dsamples synthesized at high pressure. All samples were single-phase with orthorhombic,Pbnm, structure entire range of contents achieved, 0≤3+d≤3.066. The unit-cell volume decreases increasingd, confirming that holes are doped uniformly. magnitoresistive transition temperatures increase intially increasing but decrease larger amounts ofd>0.008. Magnetic moment per Mn increasingdin agreement hole doping given byh=x+2d. Structural and physical properties consistent defect model vacancies on (La, Ca) sites in equal number,ν∼d/(3+d). Results indicate a small vacancy concentration metal sites,ν<0.003, does not produce major structural or electronic effects other than increasesTc. For concentrations, scattering defects may be cause observed broadening ofTc.