Aishwarya Krishnamoorthy, Maruthasalamoorthy Selvam, Thenmozhi Ramalingam, Mani Jayaraman, Anbalagan Gopalakrishnan, Nirmala Rajkumar, Navaneethan Mani, Rangaswamy Navamathavan
Department of Physics, School of Advanced Sciences, Vellore Institute of Technology (VIT) Chennai, Vandalur-Kelambakkam Road, Chennai 600127, India.
Department of Nuclear Physics, University of Madras, Chennai 600025, India.
ACS Omega. 2024 Jul 31;9(32):35088-35099. doi: 10.1021/acsomega.4c05361. eCollection 2024 Aug 13.
In this study, bismuth ferrite (BFO) and copper-added BFO were synthesized using the coprecipitation method. The incorporation of copper into the BFO lattice led to a reduction in the phase percentage of BFO due to the early formation of CuBiO. X-ray diffraction analysis revealed a decrease in crystallite size up to 0.1 CBFO, followed by an increase. This reduction in crystallite size causes an imbalance between the spins of the sublattices, resulting in an antiferromagnetic core/ferromagnetic shell (AC/FS) structure. The uncompensated spins generated by the decreasing crystallite size weaken the ferromagnetic properties with the addition of Cu. Additionally, the reduction in crystallite size leads to decreased electrical conductivity due to carrier scattering, with the maximum conductivity observed in BFO attributed to its volatilization. The Seebeck coefficient enhancement in 0.1 and 0.15 CBFO indicates an energy filtering effect caused by barriers at the phase boundaries. The introduction of Cu into the BFO matrix also results in reduced lattice thermal conductivity due to active centers for phonon scattering created by Cu-induced defects. The lowest lattice thermal conductivity was observed in 0.1 CBFO, which is attributed to the significant reduction in crystallite size and the presence of phase boundaries enhancing phonon scattering. The highest thermoelectric figure of merit (zT) was achieved in thermally unstable BFO due to Bi volatilization, which was mitigated by the formation of CuBiO in CBFO.
在本研究中，采用共沉淀法合成了铋铁氧体（BFO）和添加铜的BFO。由于CuBiO的早期形成，铜掺入BFO晶格导致BFO的相百分比降低。X射线衍射分析表明，微晶尺寸减小至0.1 CBFO，随后增大。微晶尺寸的减小导致亚晶格自旋之间的不平衡，从而产生反铁磁核/铁磁壳（AC/FS）结构。随着Cu的添加，微晶尺寸减小产生的未补偿自旋削弱了铁磁性能。此外，微晶尺寸的减小由于载流子散射导致电导率降低，BFO中观察到的最大电导率归因于其挥发。0.1和0.15 CBFO中塞贝克系数的增强表明相界处的势垒引起了能量过滤效应。将Cu引入BFO基体还由于Cu诱导缺陷产生的声子散射活性中心而导致晶格热导率降低。在0.1 CBFO中观察到最低的晶格热导率，这归因于微晶尺寸的显著减小和相界的存在增强了声子散射。由于Bi挥发，在热不稳定的BFO中实现了最高的热电优值（zT），而在CBFO中形成CuBiO减轻了这种情况。
