Lamhani Mohammed, Chchiyai Zakaria, Elomrani Abdelali, Manoun Bouchaib, Hasnaoui Abdellatif
Sultane Moulay Slimane University of Beni Mellal, FPK, Laboratory of Materials, Mathematics and Environment Sciences (LS2ME), 25000, Khouribga, Morocco.
Hassan First University of Settat, FST, Rayonnement-Matière et Instrumentation, S3M, 26000, Settat, Morocco.
Phys Chem Chem Phys. 2022 Aug 17;24(32):19414-19431. doi: 10.1039/d2cp01096h.
Calcium manganite (CaMnO) has been extensively utilized in many applications due to its unique physical and chemical properties. In this study, the effect of Sr-substitution at the Ca-site on the structural, magnetic, electronic and electrical properties of CaMnO manganite perovskites is investigated in detail. The perovskite compounds CaSrMnO ( = 0, 0.25, 0.5, 0.75 and 1) were synthesized through the sol-gel method at 1200 °C. From the patterns of X-ray diffraction, it was observed that all of the synthesized compounds show a pure perovskite phase at room temperature. The refinement results of the perovskite series suggest that a structural transformation from an orthorhombic () to a hexagonal (6/) system occurred for 0.50 < ≤ 0.75. We note however that the sample with the composition = 0.50 showed a phase mixture of orthorhombic () and hexagonal (6/). Based on DFT calculations, we have demonstrated the energetic stability of all compounds by negative formation energy and confirmed the semiconductor behavior by the presence of a band gap. The change in the band gap value with the Sr content suggests the potential tuning of the electronic behavior of CaMnO-SrMnO solid solution. Furthermore, as the temperature increases from 300 to 1000 K, the electrical resistivity exhibits a reduction while the Seebeck coefficient () shows an augmentation. The negative values of indicated the n-type-semiconductor nature of all compounds. The obtained values of the activation energy from thermal evolution of resistivity suggested that the electrical transport behavior of all the compounds followed the mechanism of small polaron hopping. Power factor is greatly affected by the Sr amount and reached a maximum value at = 0.50. Overall, introducing Sr into the CaMnO matrix improved the power factor and reduced electrical resistivity. According to the obtained results, the studied manganite perovskites could be proposed as suitable materials for photocatalytic and thermoelectric applications.
钙锰矿（CaMnO）因其独特的物理和化学性质而在许多应用中得到广泛应用。在本研究中，详细研究了Ca位上Sr取代对CaMnO钙钛矿锰氧化物的结构、磁性、电子和电学性质的影响。通过溶胶-凝胶法在1200℃合成了钙钛矿化合物CaSrMnO（= 0、0.25、0.5、0.75和1）。从X射线衍射图谱观察到，所有合成的化合物在室温下均呈现纯钙钛矿相。钙钛矿系列的精修结果表明，当0.50 < ≤ 0.75时，发生了从正交（）到六方（6/）体系的结构转变。然而，我们注意到，组成 = 0.50的样品呈现正交（）和六方（6/）的相混合物。基于密度泛函理论（DFT）计算，我们通过负形成能证明了所有化合物的能量稳定性，并通过带隙的存在证实了半导体行为。带隙值随Sr含量的变化表明CaMnO - SrMnO固溶体电子行为的潜在调控。此外，随着温度从300 K升高到1000 K，电阻率降低而塞贝克系数（）增大。的负值表明所有化合物均为n型半导体性质。从电阻率的热演化获得的活化能值表明，所有化合物的电输运行为遵循小极化子跳跃机制。功率因数受Sr含量的影响很大，在 = 0.50时达到最大值。总体而言，将Sr引入CaMnO基体中提高了功率因数并降低了电阻率。根据所得结果，所研究的钙钛矿锰氧化物可被提议作为光催化和热电应用的合适材料。
