Tuning paradigm of external stimuli driven electronic,optical and magnetic properties in hybrid perovskites and metal organic complexes

We have witnessed a wide range of theoretical as well as experimental investigations to envisage external stimuli induced changes in electronic, optical and magnetic properties in the metal organic complexes, while hybrid perovskites have recently joined this exciting league of explorations. The flexible organic linkers in such complexes are ideal for triggering not only spin transitions but also a plethora of various different responses under the influence of various external stimuli like pressure, temperature and light. A diverse range of applications particularly in the field of optoelectronics, spintronics and energy scavenging have been manifested. The hysteresis associated with the light induced transitions and spin-crossover governed by pressure and temperature, are promising phenomena for the design principles behind memory devices and optical switches. The pressure induced optical properties tuning or piezochromism has also emerged as one of the prominent areas in the field of hybrid perovskite materials family. It is thus imperative to have a clear understanding of how the tuning in electronic, optical and magnetic properties occur under various stimuli, and selectivity of the stimulus could be influential behind the maximum efficiency in the field of energy and optoelectronic research, and in what future directions this field could be driven from the perspective of futuristic material properties. This review though primarily focuses on the theoretical aspects of understanding the different mechanisms of the phenomena, does provide a unique overview of the experimental literature too, accompanied by the theoretical understanding such that relevant device applications can be considered through a future roadmap of tuning paradigm of external stimuli. It also provides an insight as to how energy and memory storage may be combined by using the principles of spin transition in metal organic complexes.     

稀土Dy掺杂SrFe_(12)O_(19)永磁铁氧体的结构与性能

研究了掺杂稀土Dy对锶铁氧体制备工艺、结构与性能的影响关系。研究表明,取向磁场对铁氧体磁性能的影响十分显著:随着取向磁场强度的增加,锶铁氧体晶粒发生的晶面择优取向度也增大,剩磁Br、最大磁能积(BH)max和矫顽力Hc均有上升趋势。烧结温度的影响则较复杂:随着烧结温度的增加,剩磁Br和最大磁能积(BH)max均有上升趋势,而矫顽力Hc则呈下降之势。通过在Y30牌号SrFe12O19预烧料基础上掺杂0.2%Dy2O3,经700kA/m磁场、4414N/cm2压力湿法成型的样品在1230℃温度下烧结1h后的磁性能达到了Br=398mT、Hcj=254kA/m和(BH)max=29.1kJ/m3,它与不掺杂Dy2O3的样品相比分别提高了12mT、31kA/m和0.7kJ/m3。     

Ba缺位型稀土氧化物La0.65BaxMnO3的磁电特性分析

制备了Ba缺位型稀土氧化物La0.65BaxMnO3材料,发现随着Ba缺位量在La0.65BaxMnO3中的增加,材料由高晶体对称性向低晶体对称性转移.x＞0.30时材料保持立方晶体结构,当x≤0.25时材料呈现菱方晶体结构.在La0.65BaxMnO3中,随Ba成分x从0.35减少到0.33,居里温度有一个小峰,室温电阻率有一小谷;随x进一步减小(x≤0.30),居里温度随之下降,室温电阻率上升.极化子电阻模型分析表明在La0.65BaxMnO3中,电子活动能力(x=0.35)＞电子活动能力(x=0.25)＞电子活动能力(x=0.20).这与室温电阻率的Ba成分依赖关系吻合.我们还基于迪尼模型计算了La0.65BaxMnO3中电阻随温度的变化关系曲线.计算结果与实验数据符合的较好.计算结果还表明:晶格效应、电-声作用、载流子-晶格(缺陷)耦合作用在解释稀土锰基氧化物材料中的电输运现象方面必须予以考虑.     

Optical properties of zirconia doped with yttria and some rare earth oxides

Nanometric powders of cubic zirconia stabilized with yttria and rare element oxides (Sm, Nd, Gd) were prepared by crystallization under hydrothermal conditions. The powders were uniaxially compacted, repressed isostatically, pressure-less sintered in oxygen atmosphere and hot isostatically pressed under 300 MPa Ar atmosphere. Fully dense samples were polished from both sides. The optical properties were analyzed based on the spectral dependence of the transmittance (T) and reflectance (R). Spectroscopic measurements have shown that all materials fabricated in the present work are highly transparent, with total transmission above 90% towards the long-wavelength end of the near-IR range of the spectrum. Discussion of these results will be given.     

Near-neighbour impurity effect on the spin-state transitions in LaCoO3 at low temperature (12<T<300 K)

The low-temperature magnetic susceptibility behaviour of LaCoO₃ prepared under different conditions as well as substituted samples such as LaCo_0.95M_0.05O₃ (M=Al, Ga, Cr, Fe, Mn, Ni) and La_0.98Sr_0.02CoO₃ have been investigated in the temperature range 12–300 K. Earlier interpretations of the magnetic susceptibility have been reexamined. In the case of LaCoO₃ samples containing Al, Ga, Cr and Fe impurities spin-state transitions involving a temperature independent activation energy (∼0.01 eV) are observed atT<200 K. Analysis of the data indicates that either the excited state has an intermediate-spin (t _2g ⁵ e _g ¹ ) configuration or only half the Co ions are involved in the activated transition to the high-spin (t _2g ⁴ e _g ² ) configuration. Al³⁺, and Cr³⁺ increases the activation energy considerably. Substitution of L ≠ 0 ions such as Mn³⁺ and Ni³⁺ or Co⁴⁺ (low-spin) seems to introduce ferromagnetic interactions and stabilizes the paramagnetic state. LaCoO₃, when Co is substituted by Mn (5%) or La is substituted by Sr (2%) show giant magnetic moments. When Co is substituted by Ni (5%) a ferromagnetic ground state is observed. Communication No. 226 from the Solid State and Structural Chemistry Unit.     

稀土ErCrO_3多铁性材料的结构与温度依赖的磁特性研究

系统研究了稀土ErCrO3铬氧化物的结构与磁特性,结果表明,室温下实验样品ErCrO3呈正交的单相结构(Pbnm群);从热磁曲线M-T结合不同温度下的磁滞回线结果发现,在T133K的高温区体系表现出典型的顺磁特性,其直流磁化率倒数随温度的变化很好地遵从居里-外斯定律,由此拟合可给出体系的有效平均磁矩μeff=10.57μB、顺磁居里温度Tcw=-30K。随温度降低,在133K以下样品呈现出弱铁磁的Г4(Fx)相,即铁磁相变温度为TN≈133K;当温度进一步降低到约20K,样品ErCrO3经历了从Г4(Fx)弱铁磁到反铁磁相Gy或Г1(0)的转变,并呈现出自旋重新取向特征;结合ErCrO3结构特征,这一温度依赖的复杂磁特性反映了Cr3+-Cr3+、Cr3+-Er3+和Er3+-Er3+离子之间的交换耦合作用。     

FeCoBSiNb (Y)合金的玻璃形成能力及磁性能研究

采用铜模真空吸铸法、X射线衍射仪(XRD)、示差扫描量热分析仪(DSC)及振动样品磁强计(VSM),研究稀土元素Y及Fe/Co比例变化对FeCoBSiNb(Y)系合金的玻璃形成能力、热稳定性及磁性能影响.实验结果表明,添加4%(原子分数)的Y有利于(Fe0.5 Co0.5)72B19.2 Si4.8Nb4合金玻璃形成能...     

稀土Ce对Fe-6.9%Si钢的弯曲性能与软磁性能的影响

为研究稀土Ce元素对高硅钢弯曲性能与软磁性能的影响,本文在Fe-6.9%Si钢中添加微量的稀土Ce,在650 ℃进行温轧实验,利用DSC、TEM、XRD、磁性测量和三点弯曲测试技术研究了稀土Ce对0.3 mm厚Fe-6.9%Si钢薄板的有序结构、织构、弯曲性能与软磁性能的影响。结果表明:稀土Ce的添加降低了DO₃-B2相完全转变温度,Ce原子的邻近位置会产生晶格畸变区域,限制了B2有序结构中的Fe、Si原子向近邻位置空位扩散,降低了高硅钢中有序相含量。温轧板的三点弯曲断裂挠度值由9.8 mm增加至16.1 mm,提升了高硅钢的塑性变形能力。添加稀土Ce的退火板的织构取向聚集在易磁化的λ取向线上,难磁化的γ纤维织构强度减弱,磁滞损耗降低,引起磁感应强度(B₈, B₅₀)提高,铁损值(P10/50, P10/1000)减小。     

不同稀土元素掺杂M型钡铁氧体超微粉末的磁性研究

利用溶胶－凝胶自蔓延高温合成法制备了4种稀土元素（La、Nd、Sm、Gd）掺杂钡铁氧体超微粉末。就烯土元素的种类、稀土掺杂量、合成工艺条件对钡铁氧体磁学性能的影响进行了较系统的研究。采用振动样品磁强计对粉末的磁学性能进行了检测。     

钙钛矿材料La0.65Ca0.35Mn1-xFexO3的低场磁电阻特性探讨

我们制备了氧化物材料科La0.65Ca0.35Mn1-xFexO3(x=0,0.01,0.02,0.03),研究了材料在低场0.57T下的磁电阻效应,我们发现氧化物材料La0.65Ca0.35Mn1-xFexO3据里温度Tc及电阻峰位温度Tp均值铁含量的增加而下降,这主要是因为Fe离子不参加双交换作用,且阻挡了双交换作用的进行,材料的铁磁作用随铁含量增加而减弱。利用迪尼模型计算了La0.65Ca0.35Mn1-xFexO3材料在零场及磁场为0.57T下电阻随温度的变化关系,理论计算结果与实验数据吻合得较好。     

Effect of heat treatment and composition on the superconductivity in Pb-Sr-R-Ca-Cu-O oxide system

The effect of compositions, sintering temperatures and furnace atmospheres on the superconducting transition temperatures of several members of the series Pb₂Sr₂R_1−x Ca _x Cu₃O _z (0.0⩽x⩽0.7, R=Y, Gd) has been studied. The effect of partial replacement of Pb, Ca and Y by In has also been studied. The shapes of the resistivity-temperature curves and the zero resistance temperatures are found to be extremely sensitive to the synthesis parameters employed. Superconductivity is not observed in samples treated in oxidizing atmosphere or heated at very high temperatures. Samples sintered in flowing nitrogen showed incomplete transition in resistivity starting at about 75 K and extending down to 15 K. A new and comparatively simple synthesis procedure involving treatment of the samples in vacuum has been employed to obtain nearly single-phase materials showing metallic behaviour. Using this procedure, samples of the above composition, but containing no Ca(i.e. Pb₂Sr₂RCu₃O_z, R=Y and Dy), are also found to be superconducting with zero resistance up to 48 K.     

Fe或Cr单原子链填充Cu纳米管的稳定性与磁性

基于密度泛函理论框架下的第一性原理计算,系统地研究了过渡金属(TM)Fe或Cr线性单原子链填充(6,6)Cu纳米管(Fe@CuNT或Cr@CuNT)所形成复合结构的稳定性、磁性和电子特性。相对于孤立单原子链的单原子平均结合能,Fe@CuNT和Cr@CuNT复合结构的平均结合能大大增加,表明Cu纳米管的包裹使Fe或Cr单原子链的稳定性显著增强。外部Cu原子与内部TM原子间的化学键表现出非局域金属键特性,Fe@CuNT和Cr@CuNT复合结构的磁基态分别为为铁磁态和反铁磁态。对Fe@CuNT和Cr@CuNT复合结构内部Fe原子和Cr原子的自旋磁矩和轨道磁矩进行了计算。相对于自由单原子链,Fe@CuNT和Cr@CuNT复合结构的磁晶各向异性能显著增强,因此Fe@CuNT和Cr@CuNT复合结构可应用于超高密度磁存储中。Cu纳米管的包裹使Fe@CuNT复合结构的易磁化方向相对于自由Fe单原子链的易磁化方向发生了改变。此外,Fe@CuNT复合结构在费米能级处较高的自旋极化率使其可应用于自旋电子器件中。     

Y2O3与Gd2O3共掺杂SrZrO3热障涂层材料的热物理性能

采用固相反应法合成了5mol%Y2O3与5mol%Gd2O3共掺杂SrZrO3(Sr(Zr0.9Y0.05Gd0.05)O2.95,SZYG)粉末.采用X射线衍射(XRD)和差示扫描量热仪(DSC)分别研究了SZYG粉末在1450℃长期热处理后以及200~1400℃范围内的相稳定性.采用高温热膨胀仪测量了SZYG块材的热膨胀系数,结果表明:通过Y2O3与Gd2O3共掺杂改性可以明显抑制SrZrO3的相转变.在1000℃下SZYG块材的热导率是～1.36 W/(m.K),与SrZrO3和8YSZ块材相比降低~35%SZYG分别与8YSZ和Al2O3在1250℃热处理24 h表现出很好的化学相容性.     

Osteoblast and stem cell response to nanoscale topographies: a review

To understand how cells respond to the nanoscale extracellular environment in vivo, cells from various sources have been cultured on nanoscale patterns fabricated using bottom-up and top-down techniques. Human fetal osteoblasts (hFOBs) and stem cells are some of them and they are known to be overtly responsive to nanoscale topographies – allowing us to investigate the hows and whys of the response in vitro. Information gathered from these in vitro studies could be used to control the cells, i.e. make the stem cells differentiate or retain their characteristics without the use of medium supplements. In this review, hFOB and stem cell responses to nanotopographies are summarized and discussed to shed some light on the influence of patterns on the reactions. Although both types of cells are responsive to nanoscale topographies, the responses are found to be unique to topographical dimension, shape, orientation and the types of cells used. This implies that cellular responses are influenced by multitude of factors and that if done right, cheaper self-assembled nanotopographies can be tailored to control the cells. A new self-assembly, powder-based technique is also included to provide an insight into the future of nanofabrication.     

二元及三元过渡金属氧化物的制备及其电化学应用研究进展

二元及三元过渡金属氧化物由于其优异的物理和化学特性,在电化学领域得到了广泛的应用。本文主要介绍了不同元素组成的二元及三元过渡金属氧化物,以及通过不同制备方法得到的空心球状、管状、片状、立方体、棒状、针状、伞形等多种不同形貌的二元及三元过渡金属氧化物;总结了二元及三元过渡金属氧化物在超级电容器、锂离子电池和传感器领域中表现出的优异性能;最后对二元及三元过渡金属氧化物的应用前景进行了展望。     

制冷机用稀土磁性材料及其形状尺寸与加工

在概述了近年来制冷技术中应用较多的稀土磁性材料的基础上，介绍了这些材料在应用过程中形状与尺寸的确定思路和方法以及所采用的加工工艺。     

Luminescence of Bi3+ in the orthorhombic perovskites CaB4+O3 (B4+=Zr,sn): Crossover from localized to D-state emission

The optical properties of Bi³⁺ in the orthorhombic perovskites CaZrO₃ and CaSnO₃ are investigated. The Stokes shift of Bi³⁺ emission in CaZrO₃ is small (∼0.80 eV) with the peak wavelength of the emission band occurring in the ultraviolet. This emission is attributed to the localized ³P_0,1 → ¹S₀ optical transition. In contrast, the Stokes shift of the Bi³⁺ emission in CaSnO₃ is large (>1 eV) with the emission band peaking in the visible. The emission band is also considerably broadened in CaSnO₃. It is claimed that Bi³⁺ luminescence in CaSnO₃ corresponds with the Bi³⁺ (6s²) -Sn⁴⁺ (5s^°) charge transfer emission (D-state emission). The energy of the ¹S₀→³P₁ (A-band) excitation band in both perovskites are very nearly the same. Physical reasoning is advanced for the occurrence and lack thereof of the D-state emission in these perovskites.     

非晶稀土——过渡金属磁光薄膜热稳定性研究

采用射频磁控溅射方法制备非晶ＤｙＦｅＣｏ磁光薄膜。样品的克尔回线、转矩曲线的测试显示，薄膜具有优良的磁和磁光性能。退火研究表明，随着退火时间的增加，矫顽力下降，垂直磁各向异性能减少，但克尔角变化不明显，其内在机制与薄膜中的微缺陷和应力的弛豫过程有关。