(Nd2-xAx)MnO4 (A = Ca, Sr, Ba) 製備、結構與特性研究

Preparation, structure and properties of (Nd2-xAx)MnO4 (A = Ca, Sr, Ba) compounds

陳杰泰(Chieh-Tai Chen)

指導教授 ： 高惠春

淡江大學/理學院/化學學系碩士班/碩士(2005年)

https://doi.org/10.6846/TKU.2005.00748

摘要

本研究利用聚合的多質子酸先驅物法製備了(Nd2-xAx)MnO4 (A = Ca, Sr及Ba) 三系列的樣品，獲得最佳的燒結溫度為1450℃，時間為2 h。當A = Ca、Sr及Ba時，取代的範圍分別為1.40 ≦x≦ 1.70、1.30 ≦x ≦ 1.70及1.30 ≦x ≦1.50。鈣系列樣品的晶體結構對稱性為正交晶系，空間群為Fmm2；鍶系列樣品則為四方晶系，空間群為I4/mmm。兩系列樣品皆具有K2NiF4型的結構。XANES吸收光譜得知，隨著取代量增加，三個系列樣品錳的平均價數皆隨取代量增加而增加。SEM觀察得知，隨著取代量增加，鈣、鋇兩系列樣品顆粒變大；鍶系列樣品則是顆粒變小。電阻率(ρ)量測顯示鈣系列樣品中，(Nd0.5Ca1.5)MnO4有最大的磁阻比例值{∣[ R (H, T)-R (0, T) ] ∣/ R (0, T)} × 100%，在95 K時達69%；在鍶系列樣品中則是(Nd0.4Sr1.6)MnO4有最大的磁阻比例值，在85 K時達85%。此外，鍶、鋇兩系列樣品在低溫下可能有自旋玻璃態產生。

關鍵字

磁化率 ； 多質子酸先驅物法

並列摘要

In this research, polycrystalline samples of (Nd2-xAx)MnO4 (A = Ca, Sr and Ba) with 1.40 ≦ x ≦ 1.70 for Ca, 1.30 ≦x ≦ 1.70 for Sr and 1.30 ≦ x ≦ 1.50 for Ba were synthesized by a polymeric polyprotic acid precursor method at 1450℃, 2 h. For A = Ca, single phase materials have orthorhombic symmetry with space group of Fmm2. For A = Sr, single phase materials have tetragonal symmetry with space group of I4/mmm. They all have K2NiF4 structure. Increasing x, valence of Mn4+ increases for all of the samples measured by the XANES. Increasing x, the grain size increases for the Ca and Ba series and decreases for the Sr series samples. In the Ca series, (Nd0.5Ca1.5)MnO4 has the largest magnetoresistance ratio {∣[ R (H, T)-R (0, T) ]∣/ R (0, T)} × 100%, which reaches to 69% at 95 K. In the Sr series, (Nd0.4Sr1.6)MnO4 has the largest magnetoresistance ratio, which reaches to 85% at 85 K. In addition, spin glass state probability exists at low temperature for the Sr and Ba series samples.

並列關鍵字

magnetoresistance ； K2NiF4 structure ； Rietveld analysis

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