Hussain Shahzad, Asim Muhammad, Naveed-Ul-Haq M, Rafique Mohsin, Tabassam Lubna, Arif Saira, Webers Samira, Rehman Azizur
Department of Physics, COMSATS University Islamabad, 45550, Pakistan.
Department of Physics, COMSATS University Islamabad, Lahore Campus 54000, Pakistan.
Dalton Trans. 2019 Jul 21;48(27):10275-10287. doi: 10.1039/c9dt00992b. Epub 2019 Jun 17.
The search for new multiferroic materials is on the rise due to their potential applications in an advanced generation of highly efficient multifunctional devices. Here we report a series of PbTiFeO (0 ≤x≤ 0.5) samples prepared by a solid-state reaction method. Structural analysis suggests that doping of Fe introduces oxygen vacancies along the c-axis (aliovalent substitution; Fe→ Ti), local distortions and microstrains in the PbTiO lattice which triggered the partial structural transformation from tetragonal to cubic. This has been confirmed using structural analysis tools such as X-ray diffraction, Fourier Transform Infrared Spectroscopy, Raman spectroscopy, and Mössbauer spectroscopy. The presence of oxygen vacancies was further confirmed by refining the site occupancies through Rietveld refinement. Mössbauer measurements confirmed that Fe ions exist in the 3+ state and change in coordination of some Fe ions from octahedral to tetrahedral points towards the oxygen deficiency in the system. Raman studies confirm the presence of all ordinary and quasi phonon modes in Fe doped PbTiO samples. The overlapping and weakening of modes are related to the structural changes/transformation. The modes' shifting to lower wavenumbers is ascribed to the increase in the average atomic mass at Ti-sites. The induced ferromagnetism in the system increases with an increase in the Fe content and can be explained on the basis of the F-center exchange mechanism. Moreover, we found an anomalous temperature-dependent trend in the magnetic coercivity (decrease in coercivity as the temperature is decreased) which can be explained in terms of a low-temperature decrease in an effective magnetic anisotropy when the effects of magneto-electric coupling are included. The existence of well-developed ferroelectric and ferromagnetic hysteresis loops confirmed the multiferroic nature of the system. The increase in the value of the dielectric constant at 1 MHz with an increase in the Fe content is attributed to the increase in resistivity of the system due to the formation of immobile defect dipole complexes.
由于新型多铁性材料在新一代高效多功能器件中具有潜在应用，对其的研究正在兴起。在此，我们报道了一系列通过固态反应法制备的PbTiFeO（0≤x≤0.5）样品。结构分析表明，Fe的掺杂沿c轴引入了氧空位（异价取代；Fe→Ti），在PbTiO晶格中产生了局部畸变和微应变，从而引发了从四方相到立方相的部分结构转变。这已通过X射线衍射、傅里叶变换红外光谱、拉曼光谱和穆斯堡尔光谱等结构分析工具得到证实。通过Rietveld精修对位点占有率进行精修，进一步证实了氧空位的存在。穆斯堡尔测量证实Fe离子以3+态存在，并且一些Fe离子的配位从八面体变为四面体，这表明体系中存在氧缺陷。拉曼研究证实了Fe掺杂的PbTiO样品中所有普通声子模式和准声子模式的存在。模式的重叠和减弱与结构变化/转变有关。模式向低波数的移动归因于Ti位点平均原子质量的增加。体系中诱导的铁磁性随Fe含量的增加而增强，这可以基于F中心交换机制来解释。此外，我们发现磁矫顽力存在异常的温度依赖性趋势（随着温度降低矫顽力减小），当考虑磁电耦合效应时，这可以用低温下有效磁各向异性的降低来解释。发育良好的铁电和铁磁滞回线的存在证实了该体系的多铁性本质。随着Fe含量的增加，1 MHz时介电常数的增加归因于由于形成了固定的缺陷偶极复合体导致体系电阻率的增加。
