Lin Tzu-Chiao, Qi Xiaoding
Department of Materials Science and Engineering, National Cheng Kung University, Tainan City 70101, Taiwan.
Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan City 70101, Taiwan.
Materials (Basel). 2022 Sep 25;15(19):6652. doi: 10.3390/ma15196652.
EuBaTiMO (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu/Eu and Ti/Ti in EuTiO and EuBaTiO, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co/Ni in EuBaTiO resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti numbers and an increase in Eu numbers. On the other hand, Ba doping led to an increased lattice parameter due to its larger ionic size than Eu, whereas the Co/Ni co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. EuBaTiO exhibited a clear ferroelectricity, which persisted in the Co/Ni co-doped samples until the doping levels of = 0.05 and 0.10, respectively. EuBaTiO remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co/Ni turned the samples from antiferromagnetic to ferromagnetic with transition temperatures of 2.98 K and 2.72 K, respectively. The cause for such a transition could not be explained by the larger lattice volume, oxygen vacancies and mixed valences of Eu/Eu, which were proposed in previous works. Instead, it was more likely to arise from a large asymmetric distortion of the Eu-O polyhedron introduced by the aliovalent doping, which promotes the admixture of Eu 5d and 4f states.
EuBaTiMO（M = Co或Ni）在还原气氛下于1400°C烧结。X射线光电子能谱揭示了EuTiO和EuBaTiO中Eu/Eu和Ti/Ti的混合价态，以及一些保持电荷中性所需的氧空位。EuBaTiO中Co/Ni的共掺杂导致氧空位消失，这是由于Ti数量减少和Eu数量增加的结果。另一方面，Ba掺杂由于其离子尺寸大于Eu而导致晶格参数增加，而Co/Ni共掺杂由于离子尺寸和氧空位数量变化的综合作用导致晶格参数减小。EuBaTiO表现出明显的铁电性，这种铁电性在Co/Ni共掺杂样品中一直持续到掺杂水平分别为 = 0.05和0.10。EuBaTiO保持反铁磁性，其转变温度降低至3.1 K，但Co/Ni共掺杂使样品从反铁磁性转变为铁磁性，转变温度分别为2.98 K和2.72 K。这种转变的原因无法用先前工作中提出的较大晶格体积、氧空位和Eu/Eu的混合价态来解释。相反，它更可能源于异价掺杂引入的Eu - O多面体的大不对称畸变，这促进了Eu 5d和4f态的混合。
