Influence of local structure and metal-oxygen hybridization on the electrical and magnetic properties of alkaline earth metal (Mg2+, Ca2+, Sr2+) substituted LaFeO3 ceramics

IF 2.7 3区 物理与天体物理 Q2 PHYSICS, APPLIED Journal of Applied Physics Pub Date : 2024-09-09 DOI:10.1063/5.0222233
Subhajit Nandy, Mya Theingi, Sayan Ghosh, Keun Hwa Chae, C. Sudakar
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Abstract

Pristine and alkaline-earth metal-substituted LaFeO3 (La1−xAxFeO3−δ; x = 0 and 0.2; A = Mg2+, Ca2+, and Sr2+) sintered ceramics are prepared from nanoparticles synthesized via a low-temperature citrate sol–gel technique. X-ray diffraction studies confirm the formation of a phase-pure LaFeO3 structure without any secondary phases for all the La1−xAxFeO3−δ compositions. LaFeO3 and La0.8Mg0.2FeO3−δ ceramics show Raman active modes related to La vibration, oxygen octahedral tilting, bending, and stretching. The optical bandgap is estimated to be 2.34 eV for pure LaFeO3 and reduces to 2.23 eV for La0.8Mg0.2FeO3−δ ceramics. On the contrary, La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics show no features in Raman spectra, consistent with the observation of metallic nature and diffuse band edge without any indication of sharp band edge noted. X-ray absorption spectroscopy (XAS) studies on La-L3 and Fe-K-edges confirm the oxidation states of La3+ and Fe3+ in all these ceramics. Local structural distortions and formation of oxygen vacancies in La0.8A0.2FeO3−δ (A = Mg2+, Ca2+, and Sr2+) ceramics are discerned from XAS structure analysis compared to the pristine LaFeO3 ceramics. Magnetic measurements of La1−xAxFeO3−δ reveal weak ferromagnetic nature except for La0.8Mg0.2FeO3−δ, which shows a large magnetization of 4.6 (6.7) emu/g at 300 (5) K. The ferromagnetic behavior of La0.8Mg0.2FeO3−δ ceramics seems to originate from the modification of hybridization between Fe(3d)–O(2p), La(5d)–O(2p), and Fe(4sp)–O(2p) orbitals. An anomalous magnetic transition observed only in zero-field-cooled curves at 88 K in La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics is correlated to the formation of new electronic states containing O 2p character as discerned from pre-peak O-K-edge.
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局部结构和金属氧杂化对碱土金属(Mg2+、Ca2+、Sr2+)取代的 LaFeO3 陶瓷的电学和磁学特性的影响
通过低温柠檬酸盐溶胶-凝胶技术合成的纳米颗粒制备了原始和碱土金属取代的 LaFeO3(La1-xAxFeO3-δ;x = 0 和 0.2;A = Mg2+、Ca2+ 和 Sr2+)烧结陶瓷。X 射线衍射研究证实,所有 La1-xAxFeO3-δ 成分都形成了相纯的 LaFeO3 结构,没有任何次生相。LaFeO3 和 La0.8Mg0.2FeO3-δ 陶瓷显示出与 La 振动、氧八面体倾斜、弯曲和拉伸有关的拉曼活性模式。据估计,纯 LaFeO3 的光带隙为 2.34 eV,而 La0.8Mg0.2FeO3-δ 陶瓷的光带隙则降至 2.23 eV。相反,La0.8Ca0.2FeO3-δ 和 La0.8Sr0.2FeO3-δ 陶瓷在拉曼光谱中没有显示任何特征,这与观察到的金属性质和扩散带边一致,没有发现任何尖锐带边的迹象。对 La-L3 和 Fe-K 边缘的 X 射线吸收光谱(XAS)研究证实了所有这些陶瓷中 La3+ 和 Fe3+ 的氧化态。与原始的 LaFeO3 陶瓷相比,XAS 结构分析发现 La0.8A0.2FeO3-δ(A = Mg2+、Ca2+ 和 Sr2+)陶瓷中存在局部结构畸变和氧空位的形成。La1-xAxFeO3-δ 的磁性测量结果表明,除了 La0.8Mg0.2FeO3-δ 在 300 (5) K 时显示出 4.6 (6.7) emu/g 的大磁化率外,其他陶瓷的铁磁性都很弱。La0.8Mg0.2FeO3-δ 陶瓷的铁磁行为似乎源于 Fe(3d)-O(2p)、La(5d)-O(2p) 和 Fe(4sp)-O(2p) 轨道之间杂化的改变。在 La0.8Ca0.2FeO3-δ 和 La0.8Sr0.2FeO3-δ 陶瓷中,仅在 88 K 时的零场冷却曲线中观察到异常磁转变,这与从前峰 O-K-edge 发现的含有 O 2p 特征的新电子态的形成有关。
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来源期刊
Journal of Applied Physics
Journal of Applied Physics 物理-物理:应用
CiteScore
5.40
自引率
9.40%
发文量
1534
审稿时长
2.3 months
期刊介绍: The Journal of Applied Physics (JAP) is an influential international journal publishing significant new experimental and theoretical results of applied physics research. Topics covered in JAP are diverse and reflect the most current applied physics research, including: Dielectrics, ferroelectrics, and multiferroics- Electrical discharges, plasmas, and plasma-surface interactions- Emerging, interdisciplinary, and other fields of applied physics- Magnetism, spintronics, and superconductivity- Organic-Inorganic systems, including organic electronics- Photonics, plasmonics, photovoltaics, lasers, optical materials, and phenomena- Physics of devices and sensors- Physics of materials, including electrical, thermal, mechanical and other properties- Physics of matter under extreme conditions- Physics of nanoscale and low-dimensional systems, including atomic and quantum phenomena- Physics of semiconductors- Soft matter, fluids, and biophysics- Thin films, interfaces, and surfaces
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