Abstract

The La_1.5Sr_0.5Ni_1–yCo_yO_4+δ (y = 0, 0.1, 0.2, 0.3, 0.4) complex oxides were synthesized by the citrate-nitrate route. The phase purity of the samples was confirmed by the powder X-ray diffraction (PXRD). All studied samples possess the K₂NiF₄-type structure with space group I4/mmm. The cobalt doping in La_1.5Sr_0.5Ni_1–yCo_yO_4+δ leads to the expansion of oxygen octahedra in the ab plane and their shrinkage in the c direction, thus, decreasing the structural microstrain. The increase in cobalt concentration results in a gradual increase in oxygen over-stoichiometry, while the oxygen content in La_1.5Sr_0.5Ni_1–yCo_yO_4+δ shows weak temperature dependence. It is shown that the majority of cobalt cations in these oxides are in the Co³⁺ state in the whole temperature range studied. The fitting results for the temperature dependencies of the Seebeck coefficient show that the Ni³⁺ cations are mostly in the low-spin state in La_1.5Sr_0.5Ni_1–yCo_yO_4+δ in the range of 25–1000°C, although the increase in cobalt content leads to the non-monotonous increase in the fraction of high-spin Ni³⁺ cations at T > 600°C. The cobalt doping of La_1.5Sr_0.5Ni_1–yCo_yO_4+δ decreases total conductivity due to the increase in localization of electron holes on the 3d-metal cations.

中文翻译：

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钴掺杂对La 1.5 Sr 0.5 Ni 1 y Co y O 4 + d的理化性质的影响

摘要

通过柠檬酸-硝酸盐路线合成了La _1.5 Sr _0.5 Ni _{1- y} Co _y O _{4 +δ}（y = 0，0.1，0.2，0.3，0.4）复合氧化物。通过粉末X射线衍射（PXRD）确认样品的相纯度。所有研究样品均具有空间群为I 4 / mmm的K ₂ NiF ₄型结构。钴掺杂在La _1.5锶_0.5的Ni _{1- ý}钴_ý Ò _4所+δ导致氧八面体的在膨胀AB平面及其在c方向上的收缩，因此减小了结构微应变。钴浓度的增加导致氧的化学计量逐渐增加，而La _1.5 Sr _0.5 Ni _{1 y} Co _y O _{4 +δ}中的氧含量显示出较弱的温度依赖性。结果表明，在所研究的整个温度范围内，这些氧化物中的大多数钴阳离子均处于Co ³⁺态。塞贝克系数的温度依赖性拟合结果表明，在La _1.5 Sr _0.5 Ni _1–中，Ni ³⁺阳离子大多处于低自旋状态。_y Co _y O _{4 +δ}在25–1000°C的范围内，尽管钴含量的增加导致T > 600°C时高自旋Ni ³⁺阳离子的分数非单调增加。La _1.5 Sr _0.5 Ni _{1- y} Co _y O _{4 +δ}的钴掺杂会降低总电导率，这是由于电子空穴在3 d-金属阳离子上的位置增加所致。