|題名: ||(R0.5A0.5)BO3 (R = Gd, Yb;A = Ca, Sr;B = Mn, Ti or A = Ce, Th;B = Ni)氧化物的結構與特性研究|
|其他題名: ||Structure and properties of (R0.5A0.5)BO3 (R = Gd, Yb;A = Ca, Sr;B = Mn, Ti or A = Ce, Th;B = Ni) oxides|
|作者: ||陳俊瑋;Chen, Chun-wei|
高惠春;Kao, Huey-chuen I.
|關鍵詞: ||鈣鈦礦;巨磁阻;檸檬酸鹽先驅物法;錳氧化物;perovskite;Magnetoresistance;citrate method|
|上傳時間: ||2010-01-11 02:41:02 (UTC+8)|
|摘要: ||本研究使用聚合的檸檬酸鹽先驅物法製備(R0.5A0.5)MnO3(R = Gd, Yb; A = Ca, Sr)與(R0.5A0.5)NiO3(A = Ce, Th)樣品，使用固態法製備(R0.5A0.5)TiO3 (A = Ca, Sr)。(R0.5A0.5)MnO3系列為正交晶系；(R0.5A0.5)NiO3系列為單斜晶系。SEM圖譜顯示利用檸檬酸鹽先驅物法製備的樣品，都具有較好的均勻度，而且樣品顆粒半徑較小。經由固態法製備的樣品則粒徑較大。經由XANES光譜判定Mn及Ti都具有3價與4價的混合價數。(R0.5A0.5)MnO3系列樣品皆為絕緣態，並具有類似自旋玻璃態的性質，FC與ZFC之變溫磁化率呈現不可逆的現象。所有樣品皆有負磁阻，且爐冷樣品的磁阻較驟冷樣品為高。(R0.5A0.5)MnO3系列樣品之磁阻值在80-100 K時約為60-65%。(R0.5A0.5)NiO3系列樣品呈現順磁金屬性，最大磁阻值溫度在200 K左右，約在50-60%。(R0.5A0.5)TiO3系列樣品為順磁性，並為Mott絕緣體。|
In this research, homogeneous (R0.5A0.5)MnO3 (R = Gd, Yb; A = Ca, Sr) and (R0.5A0.5)NiO3 (A = Ce, Th) compounds with perovskite structure were synthesized by a polymeric citrate precursor method. (R0.5A0.5)TiO3 (A = Ca, Sr) was synthesized by a solid state method. (R0.5A0.5)MnO3 series samples have orthorhombic symmetry and (R0.5A0.5)NiO3 have monoclinic symmetry. The samples prepared by the polymeric citrate precursor method has a better homogeneity and the grain size is smaller than that prepared by the solid state method. Mn and Ti samples have M3+ and M4+ mixed valence state observed by XANES. The (R0.5A0.5)MnO3 samples are insulator, they has a spin-glass like property and the FC and ZFC susceptibility is irreversible. The (R0.5A0.5)NiO3 samples are paramagnetic metal. At 1 T magnetic field, both (R0.5A0.5)MnO3 and (R0.5A0.5)NiO3 have negative magnetoresistance (MR) ratio. The maximum MR ratio of (Gd0.5Ca0.5)MnO3 sample is found at 80-100 K,with a range of 60-65%. The maximum MR ratio of (R0.5A0.5)NiO3 sample is found at 180-200 K, with a range of 50- 60%. The (R0.5A0.5)TiO3 samples are paramagnetic Mott insulator.