Mn-doped polycrystalline BaTiO3

Barium titanate was doped with ≲ 1 mol % Mn and sintered in air under conditions producing grain growth. Treatment at elevated temperatures in atmospheres of various oxygen partial pressures resulted in changes in crystallographic transition temperatures and in resistivity that seemed to be associated with a change in the valence state of manganese.     

载锰活性炭纤维(SACF-Mn)的制备及对乙基硫醇吸附性能的研究ⅠSACF-Mn的制备及结构研究

制备了载锰剑麻基活性炭纤维（ＳＡＣＦ－Ｍｎ），并研究了制备条件对ＳＡＣＦ－Ｍｎ的结构及表面形态的影响。研究表明：增大锰溶液的浓度，提高ｐＨ值，高价态的锰离子都有利于ＳＡＣＦ对锰的吸附；锰化合物的阴离子类型，不仅影响ＳＡＣＦ对锰的吸附，而且对载锰后ＳＡＣＦ的表面形态的影响更显著     

Local Valence and Hole-Doping Effect on Magnetic Properties in Double Perovskite La2NiMnO6

Local valence and Ca-doping effect in polycrystalline La₂NiMnO₆ have been investigated by using X-ray diffraction, X-ray absorption spectroscopy, Raman spectrum, and magnetometry. The refinement of X-ray diffraction data shows that all the samples are crystallized in pure double perovskite phase. The refined Ni(Mn)–O bond lengths and X-ray absorption spectroscopy provide evidences that the oxidation state of Ni and Mn ions in bulk La₂NiMnO₆ has the Ni²⁺ and Mn⁴⁺ configuration and the decrease of average A-site valence caused by Ca doping is compensated by the increase of Ni valence, while Mn keeps unchanged. As the Ca-doping content increases, the peak shapes of Raman spectroscopy exhibit an increase in the linewidth and decrease in the intensity, respectively, which reveals the increase the disorder of Ni–O bond length and the decrease of Ni/Mn ordering degree. Both the paramagnetic–ferromagnetic transition temperature and the saturation magnetization exhibit decrease with the increase of Ca-doping content, which are attributed to the decrease of Ni–O–Mn bond angle and the increase of Ni/Mn antisite disorder, respectively. All those behaviors can be ascribed to the valence state change of Ni ion caused by hole doping.     

Linking Atomic Structure and Local Chemistry at Manganese‐Segregated Antiphase Boundaries in ZrO2–La2/3Sr1/3MnO3 Thin Films

This paper presents direct experimental evidence of Mn segregation at three types of antiphase boundaries in La_2/3Sr_1/3MnO₃ thin films doped with ZrO₂. The local atomic structure of these antiphase boundaries is investigated by high‐angle annular dark‐field and annular bright‐field imaging in a scanning transmission electron microscope. Chemical composition and cation valence are determined by electron energy‐loss spectroscopy. The evidence that strain relaxation and Zr_Mn substitution are driving forces for the formation of the antiphase boundaries is found in this study. Analysis of atomic structure, image contrast, Mn valence state, and Mn occupancy shows that the antiphase boundaries are charge‐neutral with minimized internal electric fields.     

Tunable control over the ionization state of single Mn acceptors in GaAs with defect-induced band bending

A scanning tunneling microscope was used to study the ionization of single Mn acceptors in GaAs(110). The ionization state switches when the GaAs valence band is bent across a Mn acceptor level. This produces a ringlike feature in STM images, whose diameter depends on the tunneling conditions and distance to charged arsenic vacancies. By varying the latter, we could tune the ionization switching, as well as quantify the contributions from tip- and vacancy-induced band bending.     

Local Structure and Valence State of Mn in Ga1?xMnxN Epilayers

Mn has been incorporated in epilayers of the large-gap semiconductor GaN grown by molecular beam epitaxy using a nitrogen plasma cell. Detailed extended X-ray absorption fine structure (EXAFS) studies of a Ga_0.98Mn_0.02N epilayer confirm that the Mn atoms substitute the Ga atoms, with an increase by 2.7% of the distance to the nearest nitrogen atoms. Near-edge spectroscopy results tend to indicate that the valence state of Mn is slightly higher than 3+, while EXAFS analysis suggests an electron transfer to the N neighbors.     

Local Structure and Valence State of Mn in Ga1−x Mn x N Epilayers

Mn has been incorporated in epilayers of the large-gap semiconductor GaN grown by molecular beam epitaxy using a nitrogen plasma cell. Detailed extended X-ray absorption fine structure (EXAFS) studies of a Ga_0.98Mn_0.02N epilayer confirm that the Mn atoms substitute the Ga atoms, with an increase by 2.7% of the distance to the nearest nitrogen atoms. Near-edge spectroscopy results tend to indicate that the valence state of Mn is slightly higher than 3+, while EXAFS analysis suggests an electron transfer to the N neighbors.     

40CrMn合金奥氏体结构及相变行为的电子理论研究

利用“固体与分子经验电子理论”的键距差分析法建立了 4 0 Cr Mn合金奥氏体的价电子结构 ,研究了合金中 Cr,Mn对其 C-曲线的影响。分析表明 :4 0钢中加入 Cr,Mn元素后 ,较强的 C-Me强键络阻碍了合金奥氏体的相变 ,从而提高了合金的淬透性 ,并引起 C曲线的拖曳效应。     

Photoelectron spectroscopy study of Mn/n-Si interfacial structure

The Mn/n-Si interfacial structure is susceptible to intermixing even at room temperature. To investigate the chemistry as a result of the intermixing, valence band and core level photoelectron spectroscopy of Mn/Si has been carried out using synchrotron radiation of 134 eV energy and Al K_α X-ray (λ = 1,486.6 Å) source. The fabricated structures have also been irradiated from swift heavy ions (Fe⁷⁺ of ~100 MeV) to investigate the ion beam mixing in such structures. Valence band photoelectron spectroscopy with 134 eV photons shows the evolution of Mn3d, Mn3p and Si2p levels with a shifting towards lower binding energy side compared to their elemental values of the binding energy. This binding energy shift shows the formation of chemical compound of Si and Mn. Evolution of Si2p core level prior to and after the swift heavy ion irradiation shows strong chemical reactivity of manganese thin film with silicon. Deconvolution of Mn3d valence band has shown the formation of silicide phase due to the hybridization of Mn3d and Si3sp states. Mn2p core level study shows that the oxide and silicide formation takes place during the growth and for successive etching, oxide part is decreasing whereas silicide part is increasing.     

烧结气氛对 Er-Mg和 Er-Mn掺杂 BaTiO3陶瓷介电性能的影响

用固相法制备了Er-Mg和Er-Mn掺杂BaTiO3陶瓷,并研究烧结气氛对其微结构和电性能的影响.XRD显示样品经不同气氛烧结后均是赝立方相,在空气中烧结Er的固溶度约3.0m01%～4.0mol%,但还原气氛会抑制Er在BaTiO3中的固溶度,导致焦绿石相Er2Ti2O7出现.SEM显示Mg能抑制Er2Ti2O7晶粒的长大,而Mn促进此第二相的晶粒生长.研究表明,烧结气氛对受主离子的固溶度的作用将改变壳芯结构中壳/芯体积比,并且Mn离子的价态随气氛变化将移动居里点,从而显著影响电容变化率温度特性.采用适当的气氛烧结能够使两种介质都满足X8R要求.     

Effect of copper doping on the crystal structure and morphology of 1D nanostructured manganese oxides

We have tried to control the aspect ratio and physicochemical properties of 1D nanostructured manganese oxides through copper doping. Copper-doped manganese oxide nanostructures have been synthesized by one-pot hydrothermal treatment for the mixed solution of permanganate anions and copper cations. According to powder X-ray diffraction and electron microscopic analyses, all the present materials commonly crystallize with alpha-MnO2-type structure but their aspect ratio decreases significantly with increasing the content of copper. Such a variation of crystallite dimension is attributable to the limitation of crystal growth by the incorporation of copper ions. X-ray absorption spectroscopic studies at Mn K- and Cu K-edges clearly demonstrate that the average oxidation state of manganese ions is increased by the substitution of divalent copper ions. Electrochemical measurements reveal the improvement of the electrode performance of nanostructured manganate upon copper doping, which can be interpreted as a result of the decrease of aspect ratio and the increase of Mn valence state. From the present experimental findings, it becomes certain that the present Cu doping method can provide an effective way of controlling the crystal dimension and electrochemical property of 1D nanostructured manganese oxide.     

Luminescent properties of YAlO3:Mn single crystalline films

The YAP:Mn single crystalline films (SCF) have been crystallized by liquid phase epitaxy (LPE) method onto YAP substrates. The cathode- (CL) and photo-luminescence (PL) spectra of the YAP:Mn SCF were analyzed for determination of the preferable valence states of manganese ions which are realized in these SCF depending on Mn content in the 0.01–0.81 at.% range. The thermoluminescence (TL) properties of YAP:Mn SCF with the different Mn content above the RT range were also examined in comparison with the properties of YAP:Mn single crystal counterpart. We show that YAP:Mn (0.01 at.%) SCF possesses effective TL properties both under α-particle and γ-quanta excitation with main TSL peaks at 130 and 195 °C. We assume that the different valence states of Mn ions are responsible for their TL properties, e.g. both emission and trapping centers in YAP:Mn are formed mainly by the different valence states of Mn ions.     

Valence State of Ru at the Mn Sites in Pr0.5Sr0.5MnO3: Thermoelectric Power and X-Ray Absorption Near-Edge Structure Spectroscopy

The Ru valence at the Mn sites in Pr_0.5Sr_0.5MnO₃ has been studied using thermoelectric power (TEP) and Ru K- and L _III-edge X-ray absorption near edge structure (XANES) spectroscopy. In comparison with TEP value at 400 K for Pr_1?xSr _x MnO₃ and Pr_0.5Sr_0.5Mn_1?xRu _x O₃, it was found that the Mn-site doped Ru is in the mixed valence state between 4+ and 5+. Ru K- and L _III-edge XANES study of Pr_0.5Sr_0.5Mn_1?xRu _x O₃ (x = 0.04 and 0.1) also confirmed the mixed valence state of Ru from the fact that XANES spectrum of the Mn-site doped Ru is in between those of tetravalent and pentavalent ruthenates. These results indicate that the change of carrier density with Ru doping is not sufficient to understand the drastic enhancement of ferromagnetism observed in Ru-doped Pr_0.5Sr_0.5MnO₃. The prime role of Ru is discussed in terms of Mn valence change and magnetic interactions between Mn and doped Ru ions.     

Effect of Mn doping on electrical properties and accelerated ageing behaviours of ternary ZVM varistors

The electrical properties and d.c. accelerated ageing behaviour of ZVM (Zn-V-Mn) ceramics were investigated with different valences and contents of Mn. The incorporation of Mn into the ZV ceramics was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against the d.c. accelerated ageing stress are significantly affected by different valences and contents of Mn. The high valence of Mn (Mn⁴⁺) in the ZVM ceramics resulted in better nonlinear properties than low valence of Mn (Mn^2·66+). Furthermore, an increase in doping level of MnO² greatly improved its nonlinear properties. The ZVM ceramics doped with 2 mol% MnO² exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27 and the leakage current density is 0·042 mA/cm², but also a good stability, in which %ΔE _{1 mA} = ?2·1%, %Δα = ?25·9% for the d.c. accelerated ageing stress of 0·85 E _{1 mA}/85°C/24 h.     

Charge Transfer at the Mn Acceptor Level in GaN

MBE-grown GaN : Mn layers with Mn doping concentrations around 10²⁰ cm^–3 were investigated by photoconductivity measurements. From electron spin resonance (ESR), Mn is known to be mostly present in the neutral Mn³⁺ or Mn²⁺ + h⁺ state, which leads to a reassignment of the known optical absorption features to charge transfer from Mn³⁺, either by direct photoionization at about 1.8 eV or by a photothermal ionization process via an excited state (Mn³⁺)^* at 1.42 V higher internal energy than the Mn³⁺ ground state. It is proposed that the Mn³⁺/Mn²⁺ acceptor level is located about 1.8 eV above the valence band edge of GaN so that the nature of the acceptor wavefunction is very different from an effective-mass-like state such as the Mn²⁺ + h⁺ complex in GaAs : Mn. According to these experimental results, the realization of carrier-mediated ferromagnetism becomes rather unlikely in not co-doped GaN : Mn.     

Valence Band Structure of Coupled Diluted Magnetic Quantum Dots

The valence band structure of double InAs/GaAs diluted magnetic vertical quantum dots has been studied in the frame of multiband k⋅p calculation. We find that due to anisotropic effective mass, the ground state can be tuned from the characteristic of heavy- to light-hole state through just changing the parameter of quantum coupling between two QDs. We also show how this crossover manifests itself in the p–d exchange interaction between hole and Mn spins.     

Electrical conductivity of doped ZnS

The electrical conductivity of doped ZnS with different impurities (Mn, Fe, Co, Ni and Cu) of various concentrations has been measured to verify the existence of ladder-like levels of ‘killers’ of luminescence. Attempts have been made to ascertain the separation between the valence band of the host ZnS and the ground state of the acceptor impurities and also to investigate the effect of various concentrations of impurities on the electrical conductivity of doped ZnS.     

Valence State of Ru at the Mn Sites in Pr0.5Sr0.5MnO3: Thermoelectric Power and X-Ray Absorption Near-Edge Structure Spectroscopy

The Ru valence at the Mn sites in Pr_0.5Sr_0.5MnO₃ has been studied using thermoelectric power (TEP) and Ru K- and L _III-edge X-ray absorption near edge structure (XANES) spectroscopy. In comparison with TEP value at 400 K for Pr_1–xSr _x MnO₃ and Pr_0.5Sr_0.5Mn_1–xRu _x O₃, it was found that the Mn-site doped Ru is in the mixed valence state between 4+ and 5+. Ru K- and L _III-edge XANES study of Pr_0.5Sr_0.5Mn_1–xRu _x O₃ (x = 0.04 and 0.1) also confirmed the mixed valence state of Ru from the fact that XANES spectrum of the Mn-site doped Ru is in between those of tetravalent and pentavalent ruthenates. These results indicate that the change of carrier density with Ru doping is not sufficient to understand the drastic enhancement of ferromagnetism observed in Ru-doped Pr_0.5Sr_0.5MnO₃. The prime role of Ru is discussed in terms of Mn valence change and magnetic interactions between Mn and doped Ru ions.     

Synthesis, self-assembly, and properties of Mn doped ZnO nanoparticles

We report here a novel process to prepare Mn doped ZnO nanoparticles by a soft chemical route at low temperature. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and manganese acetate tetrahydrate heated under reflux to 160-175 degrees C using diethylene glycol as a solvent. X-ray diffraction analysis reveals that the Mn doped ZnO crystallizes in a wurtzite structure with crystal size of 15-25 nm. These nano size crystallites of Mn doped ZnO self-organize into polydisperse spheres in size ranging from 100-400 nm. Transmission Electron Microscopy image also shows that each sphere is made up of numerous nanocrystals of average diameter 15-25 nm. By means of X-ray photoelectron spectroscopy and electron spin resonance spectroscopy, we determined the valence state of Mn ions as 2+. These nanoparticles were found to be ferromagnetic at room temperature. Monodisperse porous spheres (approximately 250 nm) were obtained by size selective separation technique and then self-assembled in a closed pack periodic array through sedimentation with slow solvent evaporation, which gives strong opalescence in visible region.     

Spin Carrier Exchange Interactions in (Ga,Mn)N and (Zn,Co)O Wide Band Gap Diluted Magnetic Semiconductor Epilayers

(Ga,Mn)N and (Zn,Co)O wide band gap diluted magnetic semiconductor epilayers have been investigated by magneto-optical spectroscopy. In both cases, absorption bands observed below the energy gap allow us to study the nature of the valence and spin state of the incorporated magnetic element. Exchange interactions between magnetic ions and carriers can be observed by analyzing the magnetic circular dichroism in transmission or the exciton Zeeman splitting in reflection for (Zn,Co)O. A first estimation of the exchange integrals can be given for both materials.