Substitution of Re7+ into CaMnO3: an efficient free electron generation dopant for tuning of thermoelectric properties,Physical Chemistry Chemical Physics

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Substitution of Re7+ into CaMnO3: an efficient free electron generation dopant for tuning of thermoelectric properties
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2017-11-14 00:00:00 , DOI: 10.1039/c7cp06805k
J. Felix Shin _{1,

2,

3} , Hongjun Niu _{1,

2,

3} , Jonathan Alaria _{3,

4,

5} , John B. Claridge _{1,

2,

3} , Matthew J. Rosseinsky _{1,

2,

3}

Affiliation

Highly dense CaMn_1−xRe_xO₃ (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 CaMn_0.98Re_0.02O₃. 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.

中文翻译：

Re ⁷⁺取代为CaMnO ₃：一种用于调节热电性能的有效自由电子生成掺杂剂

高度致密的CaMn _{1- X}重新_X ø ₃（0≤ X ≤0.04）样品通过固相合成制备的。通过晶体结构，氧含量以及电和热传输性质的表征来评估Re掺杂的效果。通过在边缘光谱附近的X射线吸收确定取代的Re的氧化态为Re ⁷⁺，并且由于形成Mn ³⁺而导致晶格膨胀和电子载流子浓度增加。。电导率和热功率在较宽温度范围内的热行为可以识别不同的传导机制：（1）110 K以下，3D可变范围跳跃，（2）110至650 K之间，小的极化子传输和（3））在650 K以上时，将在移动性边缘激活载波。根据不同的掺杂剂浓度对不同掺杂剂氧化态预期的功率因数进行评估表明，使用重七价离子的掺杂策略可在较低的掺杂剂浓度下实现峰值功率因数的可及性，从而降低了非电离杂质的量，因此与先前研究的掺杂剂相比，可提高电子替代效率，即活化载流子占标称掺杂浓度的比率。对于CaMn _0.98 Re _0.02 O _3，在947 K时ZT = 0.16（3）。与未掺杂的CaMnO ₃相比，这大约增加了两倍，并且可与报道的高密度B位置掺杂的CaMnO ₃的最高值相媲美。

更新日期：2017-11-22

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