显微拉曼成像技术在钽酸锂晶体的成分、缺陷和应力分布表征中的应用研究

采用激光共聚焦显微拉曼光谱仪分别对钽酸锂晶体进行了显微拉曼成像测试研究,以865 cm^-1特征峰峰强度对钽酸锂的成分分布进行了显微拉曼成像;以865 cm^-1特征峰半高宽对晶体中锂含量分布进行了显微拉曼成像;以750 cm^-1缺陷峰强度对晶体中的本征缺陷分布进行了显微拉曼成像;以865 cm^-1特征峰峰位置对晶体中的应力分布进行了显微拉曼成像。测试结果表明,显微拉曼成像可以很好地对钽酸锂单晶片的化学成分和组分、本征缺陷、应力等化学物理性质的微观分布进行成像,未掺杂三氧化二铁比掺杂了三氧化二铁的钽酸锂晶体的成分和锂含量分布更加均匀,未掺杂三氧化二铁和掺杂了三氧化二铁的钽酸锂晶体的本征缺陷分布皆比较均匀且很少,未掺杂三氧化二铁比掺杂了三氧化二铁的钽酸锂晶体的应力分布更加均匀,掺杂了三氧化二铁的钽酸锂晶体存在明显的应力分布集中的区域。     

Absence of ferromagnetism in ferroelectric Mn-doped BaTiO3 nanofibers

Pure and Mn-doped barium titanate nanofibers were synthesized by the electrospinning method. The morphology, microstructure and crystal structure of as-spun and annealed composite nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 850°C, we obtain nanofibers a few μm long, formed by nanoparticles of irregular shape with sizes around 100 nm. X-ray diffraction and Raman spectroscopy show that a partial phase transition from tetragonal to hexagonal takes place for BaTi_0.90Mn_0.10O₃. Vibrational phonon modes were calculated for BaTiO₃ within the density functional theory (DFT) framework. Ferroelectricity has been probed on pure and Mn-doped BaTiO₃ nanofibers, by means of piezoresponse force microscopy in an atomic force microscope, confirming the polar domain switching behavior of the fibers. The measured piezoelectric coefficient d₃₃ were 31 and 22 pm/V for BaTiO₃ and BaTi_0.90Mn_0.10O₃. Magnetic properties of the samples were probed in a superconducting quantum interference device. Diamagnetic and paramagnetic behaviors were found in pure and Mn-doped samples, respectively.     

Defect controlled diffusion of lithium ions in Mn doped V2O5 for potential applications as cathode material

With a motivation to unravel the effect of cation (Mn) doping-induced modifications in structure, charge transfer resistance, and Li-ion diffusion in V₂O₅ a systematic study using X-ray diffraction (XRD), Raman Spectroscopy and electrochemical impedance spectroscopy (EIS) has been employed using three electrodes configuration. Structural investigations using XRD suggest the selective diffusion of Mn ion towards the c-axis at a low doping percentage. Raman spectroscopy suggests the shift in 994 cm^-1 modes which substantiates the uniaxial diffusion of Mn ions. Nyquist plots show that interfacial charge transfer resistance is highest for the lowest doping i.e., 1% Mn-doped V₂O₅ and exhibits the lowest diffusion coefficient as compared to other doped V₂O₅ samples. Specific capacitance calculated from cyclic voltammetry is found to be highest for the 4% Mn-doped V₂O₅ sample. Moreover, diffusion of Lithium ions improves with an increase in doping concentration due to higher concentration of defects as evident from Δd/d and Nelson–Riley factor (NRF) for pure V₂O₅ and Mn-doped V₂O₅.     

Structural,optical, and magnetic studies of manganese-doped zinc oxide hierarchical microspheres by self-assembly of nanoparticles

In this study, a series of manganese [Mn]-doped zinc oxide [ZnO] hierarchical microspheres [HMSs] are prepared by hydrothermal method only using zinc acetate and manganese acetate as precursors and ethylene glycol as solvent. X-ray diffraction indicates that all of the as-obtained samples including the highest Mn (7 mol%) in the crystal lattice of ZnO have a pure phase (hexagonal wurtzite structure). A broad Raman spectrum from as-synthesized doping samples ranges from 500 to 600 cm^-1, revealing the successful doping of paramagnetic Mn²⁺ ions in the host ZnO. Optical absorption analysis of the samples exhibits a blueshift in the absorption band edge with increasing dopant concentration, and corresponding photoluminescence spectra show that Mn doping suppresses both near-band edge UV emission and defect-related blue emission. In particular, magnetic measurements confirm robust room-temperature ferromagnetic behavior with a high Curie temperature exceeding 400 K, signifying that the as-formed Mn-doped ZnO HMSs will have immense potential in spintronic devices and spin-based electronic technologies.     

Spectroscopic characterization of a new series of bismuth tantalate pyrochlores doped with 3d-ions

X-ray spectroscopy methods (XPS, NEXAFS) were used to study the electronic state of the ions that make up pyrochlores (sp. gr. Fd-3m, No. 227) Bi₂Mg_1-xM_xTa₂O_9+Δ (M ? Cr,Mn,Fe,Co,Ni,Cu). It has been established that doping of bismuth magnesium tantalate pyrochlore with 3d-ions does not affect the electronic state of bismuth and magnesium ions, which are found in the ionic form Bi(+3), Mg(+2). Tantalum ions are in the same charge state Ta(+5-δ) due to the characteristic shift of the energy position of peaks towards the lower energies compared to the binding energy in pentavalent tantalum oxide. An energy shift in the Ta4f and Ta5p spectra is observed for all transition ions without a strict regularity in the magnitude of the signal shift depending on the nature of the dopant. Ions of some 3d-elements in the composition of pyrochlores, according to X-ray spectroscopy, have several oxidation states, for example, Cu(+1,+2), Co(+2,+3), Mn(+2,+3), Cr(+3,+6). The iron and nickel ions predominantly have the +3 and + 2 oxidation states, respectively.     

Investigations on ferromagnetism of Li and Mn codoped LiZnN by first-principles calculations

Electronic structures and magnetic properties of Li and Mn codoped LiZnN systems were investigated by using the first-principles calculations. Mn-doped LiZnN systems preferred the antiferromagnetic states, while Mn/Li codoped LiZnN systems were ferromagnetic and more stable than the Mn-doped LiZnN systems. The magnetic moments mostly arose from Mn-3d states, which hybridized with N-2p and Li-2s states near the Fermi level. The ferromagnetic coupling was suggested to be attributed to the p-d hybridization by the Mn–N–Mn chain. The results indicated that nonstoichiometry of Li was very essential for the ferromagnetism of Li(Zn,Mn)N system.     

掺铈铌酸锂晶体的生长和表征

采用提拉法生长了掺Ce的同成分LiNbO3（Ce：CLN）晶体。X射线粉末衍射表明,掺杂并不影响晶体结构,其空间群为R3c。采用X射线荧光光谱分析方法,计算得到铈离子的有效分凝系数为0.4。室温下,晶体在700～3500nm波段的透过率达75%。利用X射线光电子谱（X-ray photoelectron spectroscopy,XPS）和Raman光谱分别表征了铈离子对铌酸锂的电子和声子结构的影响。XPS结果表明,铌离子仅存在纯的＋5价,铈离子由于浓度较小,未检测到信号。Raman光谱结果显示,除Ce：CLN晶体的A1（TO4）模波数和A1（TO1）模半峰宽较纯的LiNbO3晶体发生明显变化外,其余模都与其基本一致,表明铈离子主要进入晶格的Nb位置。     

Li and Ta-modified KNN piezoceramic fibers for vibrational energy harvesters

Piezoelectric energy harvesters (PEH) hold enormous potential for converting mechanical energy from our surrounding environment into electrical energy that can be used for powering portable electronics. Potassium sodium niobate (KNN) is one of the promising alternatives to replace lead-based piezoelectric materials. This work presents a cutting-edge demonstration of synthesis-function-device integration of piezoelectric nanofibers, where the morphology and the composition are engineered towards achieving high device output. We report a flexible nanogenerator based on electrospun Li and Ta-modified lead-free KNN nanofibers yielding a high voltage output of 5.6 V, which is around 9-fold higher than for the Mn-doped KNN nanofibers reported previously. The influence of Li and Ta-incorporation into the KNN lattice on the electromechanical coupling and the effect of a nanofiber morphology are investigated. The net-shaped KNN and Li and Ta-modified KNN nanofibers, synthesized by electrospinning of appropriate sols, maintain their structural integrity upon calcination and firing steps. The phase analysis (XRD) confirms the formation of single-phase (KNN) material. Li and Ta are found to be incorporated on the A and B-sites of the perovskite lattice, respectively. Piezo force microscopy data show the heat-treated nanofibers to exhibit multi-domain ferroelectric properties.     

Modification of barium titanate sintering via rare earth oxides addition: Dilatometric and microstructural study

In this paper, the effect of rare-earth dopants (RE: Ce, Eu, Tb, Dy, and Er) in barium titanate (BT) on the shaping, sintering and microstructure was studied aimed mainly at selecting appropriate dopant for densification delaying while preserving optimal BT characteristics. The addition of dopant oxides into suspension resulted in the reduction of the deposition kinetics. The relative density of doped green bodies was lower than pure BT and decreased with dopant concentration. Only Ce enhanced green density up to 2%. The sintering process was studied using high-temperature dilatometry. The hindering densification caused by dopants was observed, but only 5 wt % of Tb and Er in BT shifted the onset of sintering to higher temperatures that has the potential applicability of these materials in layered ceramic harvesters. The significant positive impact of doping on the microstructure was attained almost in all cases manifesting themselves in higher sintered densities and markedly lower mean grain size compared to pure BT. The XRD and Raman spectroscopy analyses confirmed incorporation of the dopants into the perovskite structure and no significant existence of RE-enriched secondary phases in the microstructure.     

Ultrafine niobate ceramic powders in the system RExLi1−xNbO3 (RE: La, Pr, Sm, Er) synthesized by polymerizable complex method

Nanopowders of lithium niobate LiNbO₃ and rare earth (RE) substituted LiNbO₃–RE_xLi_1−xNbO₃, x=0.05 (RE: La, Pr, Sm, Er) were synthesized using a simple technique as the polymerizable complex method, based on the Pechini-type reaction route. A mixed solution of citric acid and ethylene glycol with Li, Nb and RE ions was polymerized. The formation mechanism, the homogeneity and the structure of the obtained powders have been investigated by thermogravimetry, X-ray diffraction, Raman spectroscopy and scanning electron microscopy measurements. The X-ray diffraction analysis indicated the formation of perovskite-type oxides, which crystallize in rhombohedral system when the Li–Nb and Li–Nb–RE polymeric precursors were treated at temperatures as low as 500 °C for 2 h. No additional crystalline phases formed during calcinations, but shifting of the XRD peaks with the RE ion substitution for Li suggested that structural modification inside the LN is the same. The Raman spectroscopy data of LiNbO₃ substituted by RE were compared to the results of the unsubstituted system. The substitution dependence of frequency and damping in the A₁(TO₂), A₁(TO₃) and E(TO₂) modes were employed to deduce the incorporation site of RE ions in LiNbO₃.     

纳米纤维锂离子筛吸附剂的制备及表征

通过静电纺丝制备了锂离子筛负载纳米纤维。研究了聚丙烯腈（PAN）和锂锰氧化物（Li1.6Mn1.6O4）配比对纳米纤维锂离子筛吸附剂提锂性能的影响。采用扫描电镜（SEM）和BET氮气吸附法对纳米纤维锂离子筛吸附剂的形貌和比表面积进行了表征。实验结果表明,在聚丙烯腈质量分数为7%和Li1.6Mn1.6O4质量分数为10%条件下,制得的纳米纤维锂离子筛吸附剂比表面积较大、提锂性能较好,其在质量浓度为10 mg/L的氯化锂溶液中对锂离子的吸附量可达13.6 mg/g。纳米纤维锂离子筛吸附剂克服了粉末状锂离子筛的不足,对实现海水提锂具有重要的参考价值。     

Relaxor transition and properties of Mn-doped SrxBa1−xNb2O6 ferroelectric ceramics

Pure and Mn-doped Sr_xBa_1−xNb₂O₆ (SBN) ceramics were prepared by the conventional solid state reaction method and their morphology, phase structure, relaxor behavior, ferroelectric and energy storage properties were investigated to reveal the effects of Mn doping on their properties. The results show that all the samples are single tetragonal tungsten bronze structure and the Mn element having few influences on their microstructures. The dielectric constant of pure SBN samples shows a classical relaxor behavior with obvious frequency dispersion and fits well with the Vogel–Fulcher law. However, the dielectric constant of Mn-doped samples does not show frequency dispersion. Then the relaxor behaviors of both pure and doped samples were further investigated by fitting the dielectric constant to the modified Curie-Weiss law. It was found that the diffusion parameters (γ) of Mn-doped samples are close to those pure samples, which indicates that the Mn-doped samples still have relaxor characteristics even without the classical dielectric frequency dispersion. Compared with the pure samples, the Mn-doped samples have a slimmer polarization-electric field (P-E) hysteresis loop, which can also prove their relaxor behaviors. The investigations of energy storage properties reveal that the Mn-doped samples have a higher energy storage density and efficiency.     

镍钴锰酸锂三元正极材料的研究与应用

镍钴锰酸锂三元材料的化学组成最初出现在20世纪90年代末期的钴酸锂和镍酸锂的掺杂研究中,其作为独立体系材料的研发开始于2001年。在该化合物中,镍呈现正二价,是主要的电化学活性元素;锰呈现正四价,不参与电化学反应,只对材料的结构稳定性和热稳定性提供保证;钴是正三价,部分参与电化学反应,其主要作用是保证材料层状结构的规整度、降低材料电化学极化、提高其倍率性能。该材料具有比容量高、高电压下结构稳定、安全性较好等优点,是目前看来最有应用前景的一种锂离子电池正极材料。     

Mn-doped ZrO2 nanoparticles prepared by a template-free method for electrochemical energy storage and abatement of dye degradation

A template-free technique was used to prepare pure and Mn-doped ZrO₂ photocatalyst samples in this study. The effect of doping on the structural, optical, photocatalytic, and supercapacitor properties were investigated. X-ray diffraction analysis revealed that the prepared samples had a tetragonal crystal structure. The optical band gap was narrowed due to the incorporation of Mn ions. The photocatalytic activity of methyl orange organic dye degradation with the Mn-doped ZrO₂ sample was examined under visible-light irradiation. The doped sample showed 83% of dye degradation after 100 min of irradiation. Cyclic voltammetry was used to study the supercapacitor properties, and the doped samples exhibited capacitance seven times greater than that of the pure sample.     

Preparation and characterization of electrospun Ag/polyacrylonitrile composite nanofibers

Novel composite nanofibers consisting of Ag nanoparticles and polyacrylonitrile (PAN) were fabricated successfully. The Raman properties of these Ag/PAN nanofibers were studied at low temperatures, which showed good Raman characteristics. In the process, a PAN solution containing Ag ions was directly electrospun to obtain nanofiber films containing Ag ions, and the Ag ions of resulting composite nanofibers were reduced to Ag nanoparticles in N₂H₅OH aqueous solution. Then, we treated Ag/PAN composite nanofibers at 100 °C, 200 °C, 400 and 600 °C, respectively. The Ag/PAN nanocomposite film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) patterns and surface-enhanced Raman scattering (SERS) spectroscopy.     

Optical and mechanical properties of mn-doped transparent alumina and their comparison with selected rare earth and transient metal doped aluminas

Mn-doped translucent alumina prepared in this work was characterised in terms of densification process, microstructure, optical and mechanical properties. The manganese effect was compared with the influence of chromium, erbium and europium in previously prepared doped transparent alumina. Contrary to them, manganese accelerates both densification and grain growth. Real in line transmittance (RIT) at 632.8 nm and transmission/diffuse reflectance spectra in UV-VIS-NIR range of Mn-doped alumina were measured. The lower RIT values and rapidly decreased transmittance/reflectance below 800 nm are caused by relatively high absorption of light by Mn species and by increased grain size. The deep red emission of Mn⁴⁺ centres that almost fade at higher manganese concentration was indicated in photoluminescence spectra, with a decay time of ∼670 μs. The dopant introduction in all cases resulted in an increase in hardness of doped alumina up to 20 % compared to undoped alumina and a decrease in related fracture toughness.     

Effect of monovalent ions on the piezoelectric properties of (Na0.5K0.5)NbO3–(M)TaO3 ceramics

Sodium potassium niobate (NKN) ceramics modified by lithium or silver tantalates were prepared in order to compare the effect of monovalent additives and then their crystal structure, sinterability, and dielectric and piezoelectric properties were investigated with varying the amount of additives. It was clearly seen for the silver tantalate added NKN ceramics that dielectric constant, k_p and d₃₃ were dependent on the density and microstructure. While NKN ceramics added with lithium tantalate exhibited strong dependence on the existence of morphotrophic phase boundary and second phase formation rather than the density. These results were explained in terms of the phase formed and microstructure and sinterability.     

Electric‐Field‐Driven Phase Transition Process in (K,Na, Li)(Nb,Ta, Sb)O3 Lead‐Free Piezoceramics

The electric‐field‐driven phase transition in (K, Na, Li)(Nb, Ta, Sb)O₃ lead‐free piezoelectric ceramics was investigated by X‐ray diffraction, Raman spectra, and the temperature dependences of permittivity spectra. After poling under different electric fields, phase of the ceramics transformed gradually from orthorhombic–tetragonal coexisting phase to orthorhombic phase, indicating that the crystal structure of ceramics was strongly sensitive to electric field as an external stimulus. A secondary phase K₃Li₂Nb₅O₁₅ induced by electric field was detected in the ceramics with Li content of 7 mol%, which was close to the solubility limit of lithium. This field‐induced secondary phase resulted from the movement of Li ions and the structural deformation induced by electric field. Moreover, piezoelectric constant d₃₃ increased with the increasing poling field strength and the enhancement can be attributed to the field‐triggered domain switching. This study implied that in addition to temperature and composition, which has been reported in previous researches, electric field might be an effective way for inducing phase transition in lead‐free piezoelectric ceramics and improving the electrical performances simultaneously.     

Formation of lithium clusters and their effects on conductivity in diamond: A density functional theory study

We have applied Density Functional Theory (DFT) within the Generalized Gradient Approximation to study the behavior of lithium impurities in the diamond lattice. It was found that, although isolated interstitial lithium atoms in tetrahedral sites have a donor state relatively close to the conduction band at 0.35 eV, their behavior is critically affected by adjacent interstitials. Lithium atoms that occupy adjacent interstitial tetrahedral sites cluster spontaneously and induce carbon–carbon bond breaking in their neighborhood. The corresponding charge distribution and electronic density of states analyses show that charge localization takes place at the carbon atoms around the lithium clusters and deeper mid-gap states are introduced in the diamond band gap. The formation energy was found to be 1.88 eV and 3.09 eV, for clusters of two and three lithium atoms, respectively, considered in this study. The calculations also indicate that Li clustering would not take place if Li ions instead of atoms were incorporated interstitially.     

Energy and Charge Transfer Dynamics in Doped Semiconductor Nanocrystals

Doping semiconductor nanocrystals with transition metal ions introduces new optical, electronic, and magnetic properties to the host semiconductor nanocrystals. The energy transfer and charge transfer between exciton and dopant ions are the key photophysical processes responsible for the unique properties of doped semiconductor nanocrystals, which are distinct from their undoped counterparts. Since the energy transfer and charge transfer processes between exciton and dopant ions compete with the usual relaxation pathways of the exciton, competition among different dynamic processes ultimately determines the photophysical properties of doped nanocrystals. In this review, we discuss the dependence of the dynamics of the energy transfer and charge transfer processes in Mn-doped II-VI semiconductor nanocrystals on the structure of the host nanocrystal, spatial distribution of the dopant ions within the nanocrystal, and charge carrier-trapping molecules near the surface of the nanocrystals.