Relationship between crystal structure and electrical properties of the Ca-rich region in (La1-xCax)MnO2.97

Perovskite-type (La1-xCax)MnO2.97 (0.90 less than or equal to x less than or equal to 1.00) were synthesized by a standard ceramic technique. (La1-xCax)MnO2.97 exhibits the metal-insulator transition in the range 0.90 less than or equal to x less than or equal to 0.98, With increasing x, the metal-insulator transition temperature (T-t) decreases and d rho/dT increases. The decrease in both the angles for Mn-O(1 and 2)-Mn and the number of 3d electrons with increasing x makes pi-bonding weak, (La-0.02 Ca-0.98)MnO2.97(x = 0.98) has the peak at ca. 780 K in the rho-T curve, and this peak is caused by the oxygen deficiency. (C) 1996 Academic Press, Inc.