Substitution of Re7+ into CaMnO3: an efficient free electron generation dopant for tuning of thermoelectric properties.
Substitution of Re7+ into CaMnO3: an efficient free electron generation dopant for tuning of thermoelectric properties.
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DOI：
10.1039/c7cp06805k
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发表时间：
2017-11
期刊：
影响因子：
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通讯作者：
J. Shin;H. Niu;J. Alaria;J. Claridge;M. Rosseinsky
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文献类型：
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作者：
J. Shin;H. Niu;J. Alaria;J. Claridge;M. Rosseinsky
通过固相合成制备了高密度 CaMn1-xRexO3 (0 ≤ x ≤ 0.04) 样品。通过晶体结构、氧含量以及电和热传输特性的表征来评估Re掺杂的效果。通过近边X射线吸收光谱确定取代Re的氧化态为Re7+，并由于Mn3+的形成而导致晶格膨胀和电子载流子浓度增加。电导率和热电势在较宽温度范围内的热行为允许识别不同的传导机制：(1) 低于 110 K，3D 可变范围跳跃，(2) 110 至 650 K 之间，小极化子输运，以及 (3) 高于 650 K，在迁移率边缘激活载流子。对不同掺杂剂氧化态预期功率因数作为掺杂剂浓度函数的评估表明，与之前研究的掺杂剂相比，使用重七价离子的掺杂策略允许在较低掺杂剂浓度下获得峰值功率因数，降低非电离杂质的量，从而提高电子替代效率，即活化载流子与标称掺杂浓度的比率。 CaMn0.98Re0.02O3 在 947 K 时获得了更高的功率因数和更低的晶格热导率，峰值品质因数 ZT = 0.16(3)。与未掺杂的 CaMnO3 相比，这大约增加了两倍，并且与报道的高密度 B 位掺杂 CaMnO3 的最高值相当。
Highly dense CaMn1-xRexO3 (0 ≤ x ≤ 0.04) samples were prepared by solid-state synthesis. The effect of Re doping was assessed by the characterisation of crystal structure, oxygen content, and electrical and thermal transport properties. The oxidation state of the substituted Re was determined by X-ray absorption near edge spectra to be Re7+, and led to expansion of the lattice and an increase in electron carrier concentration due to the formation of Mn3+. The thermal behaviour of the electrical conductivity and the thermopower over a wide temperature range allowed identification of different conduction mechanisms: (1) below 110 K, 3D variable range hopping, (2) between 110 and 650 K, small polaron transport, and (3) above 650 K, activation of carriers over a mobility edge. Evaluation of the power factor expected for different dopant oxidation states as a function of dopant concentration shows that the doping strategy using a heavy heptavalent ion allows accessibility of the peak power factor at lower dopant concentrations, lowering the amount of non-ionised impurities, and therefore improves the electronic substitution efficiency, the ratio of activated carriers over the nominal doping concentration, compared to previously studied dopants. An increased power factor and a reduced lattice thermal conductivity are obtained with a peak figure of merit ZT = 0.16(3) at 947 K for CaMn0.98Re0.02O3. This is an approximately two-fold increase compared to undoped CaMnO3, and is comparable to the highest values reported for highly dense B-site doped CaMnO3.