Synthesis, structure and magnetic properties of R-W-O-N ( R=Nd and Eu) oxynitrides
Synthesis, structure and magnetic properties of R-W-O-N ( R=Nd and Eu) oxynitrides
复制标题
DOI：
10.1016/j.jssc.2006.09.025
复制
发表时间：
2007
影响因子：
3.3
通讯作者：
R. Pastrana-Fábregas;J. Isasi-Marín;C. Cascales;R. Sáez-Puche
中科院分区：
文献类型：
--
作者：
R. Pastrana-Fábregas;J. Isasi-Marín;C. Cascales;R. Sáez-Puche
以R_2W_2O_9为前驱体，在1173 K的氨气流中氮化24 h，合成了稀土氧化物和铕钨氮氧化物。得到的多晶氮氧化钕相的组成为NdWO3.05N0.95，晶体结构为白钨矿型结构，空间群为S.G. I41/a（#88）。类似的铕衍生物，具有分子式EuWO 1.58N1.42，呈现立方钙钛矿型结构，S. G.下午3时（#221）。通过对Nd和Eu氮氧化物的X射线粉末衍射图进行Rietveld精修，分别确定了晶胞参数a=5.255（1）nm，c=11.399（3）nm和a=3.976（3）nm。磁化率测量表明，NdWO_（3.05）N_（0.95）在50- 300 K范围内表现为顺磁性。在40 K以下偏离居里-外斯定律的现象反映了在S4晶场CF势的影响下，Nd 3+的4 I9/2基态发生分裂，成功地再现了磁化率χ− 1 mvs。T，使用半经验结构导出的CF参数，表明。EuWO_（1.58）N_（1.42）在20 K以下是顺磁性的，其有效磁矩为8.01μ B，表明该氧氮化物中存在Eu ~（2+）。在20 K下观察到的磁化率突变和饱和磁矩的6μ B值归因于亚铁磁相互作用的开始，其中Eu ~（2+）和W ~（5+）亚晶格似乎参与其中。
Neodymium and europium tungsten oxynitrides have been synthesized by the nitridation of corresponding R2W2O9precursor oxides, in ammonia flow at 1173K during 24h. The obtained polycrystalline neodymium oxynitride phase, with NdWO3.05N0.95composition, crystallizes with the tetragonal symmetry of the scheelite-type structure, space group S.G. I41/a (#88). The analogous europium derivative, with formula EuWO1.58N1.42, presents the cubic perovskite-type structure, S.G. Pm3¯m (# 221). Unit-cell parameters, a=5.255(1)Å, c=11.399(3)Å, and a=3.976(3)Å, have been established from Rietveld refinements of collected X-ray powder diffraction patterns for the Nd and Eu- oxynitrides, respectively. Magnetic susceptibility measurements show that NdWO3.05N0.95behaves as paramagnetic in a wide range of temperature T ∼50–300K. The downwards deviation from the Curie–Weiss law below 40K reflects the splitting of the4I9/2ground state of Nd3+experienced under the influence of a S4crystal field CF potential, as the successful reproduction of the magnetic susceptibility χ−1mvs. T, using semi-empirical structure-derived CF parameters, indicates. EuWO1.58N1.42is paramagnetic down to 20K, and the measured effective magnetic moment 8.01μBis indicative of the presence of Eu2+in this oxynitride. The observed sudden jump in the magnetic susceptibility at 20K and the value of 6μBfor the saturation moment is attributed to the onset of ferrimagnetic interactions in which the Eu2+and W5+sublattices appear to be involved.