Electron-Hole Asymmetry in the Rare-Earth Manganates A Comparative

Electron—Hole Asymmetry in the Rare-Earth Manganates A Comparative Study of the Hole- and the Electron-Doped Materials 

Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India, and Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India, and Materials Research Laboratory, University of California, Santa Barbara, California 93106 

Received June 6, 2000. Revised Manuscript Received December 18, 2000 

Electron—hole asymmetry is encountered in cuprate superconductors.3 In the cuprates, superconductivity occurs in the electron-doped regime, although not as prominently as in the hole-doped regime. The electron- 

Substitution of Cr3+ or Ru4+ in the Mn site of certain charge-ordered manganates is known to destroy the CO state, rendering them ferromagnetic and metallic.lc-4 8 The effect of Cr3+ doping on Pri Ca,Mn03 has been 

64Cao36Mn03,1, and Pro.36Cao.64Mn03, II, are both orthorhombic Pbnm), but the unit cell is larger in the former as expected on the basis of the relative sizes of Mn and Mn. In Table 3, we list the atomic coordinates and the lattice parameters of the two manganates obtained from the Rietveld analysis. The Mn—O distances in I are longer than those in II, but the Mn—O— Mn angles in the two are comparable. 

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