METAL-INSULATOR TRANSITION IN THE SYSTEM (ND1-XCAX)MNO2.99 (0.5 LESS-THAN-OR-EQUAL-TO X LESS-THAN-OR-EQUAL-TO 0.9)

The electrical resistivity of (Nd//1// minus //xCa//x)MnO//2//. //9//9 (0. 5 less than equivalent to x less than equivalent to 0. 9) was measured in the temperature range 80 to 850 K. At low temperature, all manganates are n-type semiconductors, and the electrical resistivity follows the Mott's T** minus ** one quarter law, indicating the possible occurrence of variable range hopping of electrons due to Anderson localization. At high temperature, all manganates exhibit a metal-insulator transition without any crystallographic change. From the results of the magnetic susceptibility, it is concluded that the metal-insulator transition is caused by a change of the spin state of trivalent manganese ion in (Nd//1// minus //xCa//x)MnO//2//. //9//9.