中文摘要：

采用溶胶-凝胶法制备了（Pr1-xLax）0．75Na0．25MnO3（0．00≤x≤1．00）系列多晶样品．X射线衍射结果表明，所有样品均为单相类钙钛矿结构，随着La^3＋离子含量的增加，样品由x≤0．50时的正交结构转变为x≥0．70时的菱面体结构．磁性测量结果表明，La^3＋离子的掺入还导致了Pr0．75Na0．25MnO3电荷有序的破坏．在x≤0．1时，电荷有序转变温度随La^3＋离子含量增加而降低；当x〉0．10时，电荷有序现象消失，样品出现顺磁-铁磁相变，同时伴随着绝缘体-金属转变．磁熵变研究表明，x≥0．5的样品在室温附近和较低磁场下具有较大的磁熵变，可望成为新的室温磁致冷材料．

英文摘要：

Polycrystalline （Pr1-xLax）0.75Na0.25MnO3（0.00 ≤ x ≤ 1.00） manganites were prepared by sol-gel method. X-ray Diffraction patterns showed that the samples are crystallized in single phase with perovskite-like structure. The structure of the compounds transforms from orthorhombic structure for x≤0.50 to rhombohedral structure for x ≥0.70. The introduction of La^3＋ ions also suppresses the charge ordering in the samples. The charge ordering transition temperature decreases with increasing La^3＋ doping when x ≤0.10. The charge ordering phenomenon disappeared for the samples with x 〉 0.10, paramagnetic-ferromagnetic transition appeared, while the insulator-metal transition can be observed. For x≥0.50, the compounds also show large magnetic entropy change under low field near or above room temperature, indicating the material can he used in magnetic refrigeration.