论文标题
观察各向异性热膨胀和双perovskites中的jahn-teller效应Sr $ _ {2-x} $ la $ _x $ conbo $ _6 $使用中子衍射
Observation of anisotropic thermal expansion and Jahn-Teller effect in double perovskites Sr$_{2-x}$La$_x$CoNbO$_6$ using neutron diffraction
论文作者
论文摘要
我们使用依赖温度的中子粉末衍射（NPD）来研究双钙钛矿Sr $ _ {2-x} $ la $ _x $ conbo $ _6 $（$ x = $ x = $ 0.4和0.6）中的结构变化和磁相互作用。从四方（$ i4/m $）到单斜胶（$ p2_1/n $）的结构相过渡，在$ x = $ 0.4和0.6个样本之间。有趣的是，单位电池参数的温度演变遵循grüneisen近似，分析表明，在$ x = $ 0.4样品的情况下，各向同性热膨胀，而$ x = $ x = $ 0.6样品显示了各向异性，其中沿着$ c $的热膨胀沿$ c $ akesis沿Grüneisen的偏差显着偏离。我们观察到COO $ _6 $中的$ z $ - jahn-teller扭曲，因此在相邻的NBO $ _6 $ contahedra中扭曲了$ z $。随着LA取代的增加，八人体失真程度的降低可以明显地从B点原子周围的局部变形参数$δ$显着降低。
We use temperature dependent neutron powder diffraction (NPD) to investigate the structural changes and magnetic interactions in double perovskite Sr$_{2-x}$La$_x$CoNbO$_6$ ($x=$ 0.4 and 0.6). A structural phase transition from tetragonal ($I4/m$) to monoclinic ($P2_1/n$) is observed between $x=$ 0.4 and 0.6 samples. Interestingly, temperature evolution of the unit cell parameters follow the Grüneisen approximation, and the analysis suggest the isotropic thermal expansion in case of the $x=$ 0.4 sample, whereas the $x=$ 0.6 sample shows the anisotropy where the thermal expansion along the $c$-axis significantly deviates from the Grüneisen function. We observe the $z$-out Jahn-Teller distortion in the CoO$_6$ and consequently $z$-in distortion in the adjacent NbO$_6$ octahedra. With increase in the La substitution, a decrease in the degree of octahedral distortion is evident from the significant reduction in the local distortion parameter $Δ$ around the B-site atoms.
