新穎三元金屬氮化物的製備、晶體結構與特性鍵定

Abstract

本研究中，我們利用金屬氧化物 AMO4 (A＝Co, Ni；M＝Mo, W)作為前驅 物，在適當溫度(600∼800℃) 下，氨解形成新穎三元過渡金屬氮化物 A3 M3N (A＝Co, Ni；M＝Mo, W)。其中 Co3M3N (M＝Mo, W) 二者具有相同的 空間群Fd3.cflex.m，粉末X光繞射數據顯示為立方結構，其晶格常數分別 為 ao＝11.020(1) Angstrom 與 ao＝11.010(1) Angstrom。 Rietveld 結構精算亦顯示：Co3M3N (M＝Mo, W) 與 Fe3Mo3N (.eta.- Fe3W3C, E93 type) 具有相同結構。另一方面，對於 Ni3M3N (M＝Mo, W)而言，二 者在結晶學上為新的結構。經初步標定(indexing) 與晶格常數計算，顯 示：Ni3Mo3N 為正交結構，晶格常數為：a＝6.635(2) Angstrom , b ＝6.668(4) Angstrom, c＝6.573(3) Angstrom。而 Ni3W3N 為立方結構 ，晶格常數 ao＝6.641(3) Angstrom。此二種新氮化物之晶體結構解析正 進行中。此外，以光電子能譜量測 N1s 訊號顯示：在Co3Mo3N中，氮確實 與金屬形成金屬氮化物。 A3M3N (A＝Co, Ni；M＝Mo, W) 等四種氮化物 ，在溫度 300∼10 K 的電阻率量測，展現典型的金屬特性，且其室溫電 阻率約在2.0∼9.0 mohm- cm之間。磁化率量測則顯示：四者在較高溫時 ，表現順磁特性，而低溫時則偏離磁化率對溫度的線性關係。此外，我們 也進行磁化曲線的研究，發現溫度在5K時 Co3M3N (M＝Mo, W) 二種氮化 物會出現磁滯現象，顯示兩者在該溫度以下可能具鐵磁性，而 Ni3M3N (M ＝Mo, W) 則無此現象。 The syntesis of novel ternary transition metal nitrides A3M3N (A ＝Co, Ni；M＝Mo, W) has been attempted by ammonolysis of corresponding AMO4 oxide precursors at temperature of 600℃ to 800℃. X-ray diffraction indicated that Co3Mo3N (M＝Mo, W) crystallize in cubic structure with space group Fd3.cflex.m (No. 227) and lattice constants ao＝11.020(1) Angstrom and 11.010(1) Angstrom for M＝Mo and W, respectively. In addition, Rietveld refinement also indicated that Co3M3N (M＝Mo, W) are isostructural with Fe3Mo3N (.eta.-Fe3Mo3C, E93 type). On the other hand, the two new nickel-containing nitrides, Ni3M3N (M＝ Mo, W) have been indexed as an orthorhonbic cell with a ＝6.635(2), b＝6.668(4) and c＝6.573(3) Angstrom for M＝Mo and a cubic cell with ao＝6.641(3) Angstrom for M＝W, respectively. The determination of crystal structure of these two nitrides are in progress. On the other hand, the X-ray photoelectron core spectra indicated that nitrogen does form metal nitrides for the title compounds based on the chemical shift of the N1s bindingrgy. The A3M3N (A＝Co, Ni；M＝Mo, W) nitrides exhibited typical metallic behavior with room temperature resistivity of 2.0∼9.0 m.OMEGA.-cm in the temperature range of 300∼10K. Temperature- dependent magnetic susceptibility (.chi. VS. T) data showed that the four title metal nitrides exhibited Curie- Weiss type paramagnetism at temperature above approximately 120K with deviation of .chi.-T from linearity at low temperature. Furthermore, the magnetization curves of the title metal nitrides were also investigated at 50K and 5K, respectively. We have found that magnetic hysteresis, indicating possible presence of ferromagnetism, was observed in the Co3M3N (M＝Mo, W) compounds at 5K only, whereas no such phenomenon was observed in the Ni3Mo3N (M＝Mo, W) compounds.