Ba（Mn_ xFe_{1-x}）_2As_2体系的大混相间隙
Large Miscibility Gap in the Ba(Mn_xFe_{1-x})2As2 System
摘要：
BaMn_2As_2和BaFe_2As_2在室温下都是体心四元ThCr_2Si_2型（122型）结构，但它们的晶胞体积和磁、电输运性质却有很大的不同。在Ba（Mn_ xFe_{1-x}）_2As_2体系中，我们发现了一个很大的能隙.对从1000 ℃缓慢冷却到室温（RT）的样品进行的粉末X射线衍射（XRD）测量的Rietveld精化揭示了对于x = 0.2、0.4、0.5、0.6和0.8，BaMn 2As 2和Ba（Mn_{0.12} Fe_{0.88}）2As 2相以及杂质相的两相混合物。我们推断在300 K时该体系存在一个能隙，其组成极限为0.12 < x < 1.对于从1000 C淬火到77 K的样品，RT XRD数据的细化表明，在RT下的可结晶性间隙在1000 C下变窄到0.2 < x < 0.8。x=0.4、0.5和0.6的样品在1100-1400 ℃淬火至77 K时，含有单一的122型相以及大量的Fe_{1-x} Mn_xAs和FeAs_2杂质相。这些结果表明，该系统不是一个伪二元系统在整个组成范围内，122型相具有显着的均匀性范围在这些温度下。本文报道了x = 0.2和0.8的单相淬火多晶样品和轻掺杂BaMn_2As_2晶体的磁化率、电阻率和热容随温度的变化。
英文摘要：
The compounds BaMn2As2 and BaFe2As2 both crystallize in the body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature but exhibit quite different unit cell volumes and very different magnetic and electronic transport properties. Evidently reflecting these disparities, we have discovered a large miscibility gap in the system Ba(Mn_xFe_{1-x})2As2. Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples slow-cooled from 1000 C to room temperature (RT) reveal a two-phase mixture of BaMn2As2 and Ba(Mn_{0.12}Fe_{0.88})2As2 phases together with impurity phases for x = 0.2, 0.4, 0.5, 0.6 and 0.8. We infer that there exists a miscibility gap in this system at 300 K with composition limits 0.12 < x < 1. For samples quenched from 1000 C to 77 K, the refinements of RT XRD data indicate that the miscibility gap at RT narrows at 1000 C to 0.2 < x < 0.8. Samples with x=0.4, 0.5 and 0.6 quenched from 1100-1400 C to 77 K contain a single 122-type phase together with significant amounts of Fe_{1-x}Mn_xAs and FeAs2 impurity phases. These results indicate that the system is not a pseudo-binary system over the whole composition range and that the 122-type phase has a significant homogeneity range at these temperatures. Magnetic susceptibility, electrical resistivity and heat capacity measurements versus temperature of the single-phase quenched polycrystalline samples with x = 0.2 and 0.8 and for lightly doped BaMn2As2 crystals are reported.
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