Electromagnetic wave absorbing properties of TMCs (TM=Ti,Zr, Hf,Nb and Ta) and high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C

Electromagnetic wave (EMW) absorbing materials play a vital role in modern communication and information processing technologies to inhibit information leakage and prevent possible damages to environment and human bodies.Currently,most of EMW absorbing materials are either composites of two or more phases or in the form of nanosheets,nanowires or nanofibers in order to enhance the EMW absorption performance through dielectric loss,magnetic loss and dielectric/magnetic loss coupling.However,the combination of complex shapes/multi phases and nanosizes may compound the difficulties of materials processing,composition and interfaces control as well as performance maintenance during service.Thus,searching for single phase materials with good stability and superior EMW absorbing properties is appealing.To achieve this goal,the EMW absorbing properties of transition metal carbides TMCs (TM=Ti,Zr,Hf,Nb and Ta) and high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C which belong to ultrahigh temperature ceramics,were investigated in this work.Due to the good electrical conductivity and splitting ofd orbitals into lower energy t2g level and higher energy eg level in TMC6 octahedral arrangement,TMCs (TM=Ti,Zr,Hf,Nb and Ta) exhibit good EMW absorbing properties.Especially,HfC and TaC exhibit superior EMW absorbing properties.The minimum reflection loss (RLmin) value of HfC is -55.8 dB at 6.0 GHz with the thickness of 3.8 mm and the effective absorption bandwidth (EAB) is 6.0 GHz from 12.0 to 18.0 GHz at thickness of 1.9 mm;the RLmin value of TaC reaches-41.1 dB at 16.2 GHz with a thickness of 2.0 mm and the EAB is 6.1 GHz with a thickness of 2.2 mm.Intriguingly,the electromagnetic parameters,i.e.,complex permittivity and permeability are tunable by forming single phase solid solution or high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C.The RLmin value of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C is -38.5 dB at 9.5 GHz with the thickness of 1.9 mm,and the EAB is 2.3 GHz (from 11.3 to 13.6 GHz) atthickness of 1.5 mm.The significance of this work is that it opens a new window to design single phase high performance EMW absorbing materials by dielectric/magnetic loss coupling through tuning the conductivity and crystal field splitting energy of d orbitals of transition metals in carbides,nitrides and possibly borides.     

Structure and magnetic properties of sputtered FePtM (M = Ti,Nb) thin films

FePt thin films doped with various Ti and Nb concentrations ranging from 2.9 to 9.1 at.% were prepared by r.f. magnetron sputtering. The structural and magnetic properties of Ti- and Nb-doped FePt thin films were investigated. Structural studies revealed that the long range ordering in FePt thin films depends on the doping concentration and annealing temperature of FePt thin films. The addition of Ti and Nb is found to enhance the grain refining in FePt thin films. The effects of doping concentration on the magnetic properties of FePt thin films were studied and discussed.     

Characterization and dielectric properties of Sr4La2Ti4M6O30 (M=Nb, Ta) ceramics

Sr₄La₂Ti₄M₆O₃₀ (M=Nb or Ta) compounds were synthesized by the conventional powder compaction and high temperature solid state reaction technique. The dielectric properties of the sintered samples were measured and they were further characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Sr₄La₂Ti₄M₆O₃₀ compounds are paraelectric phases adopting filled tetragonal tungsten–bronze (TB) structure at room temperature. Sr₄La₂Ti₄Nb₆O₃₀ and Sr₄La₂Ti₄Ta₆O₃₀ show high dielectric constants of 387 and 166 together with low dielectric loss of 0.0084 and 0.0042 at 1 MHz, respectively.     

Effects of dopants on magnetic properties of Cu-doped ZnO thin films

We report the observation of room temperature ferromagnetism (FM) in Cu-doped ZnO (ZnO: Cu) thin films synthesized by sol–gel technique. While donor Al³⁺ cations are introduced into the ZnO: Cu films, the saturation magnetization decreases rapidly. Cu 2p core-level X-ray photoelectronic spectra demonstrate that the FM is strongly correlated with Cu²⁺ cations (3d ⁹ configuration). To further study the relationship between the FM and acceptors, Na⁺ cations are also introduced into the ZnO: Cu films to increase the saturation magnetization. The enhanced FM in the (Cu, Na)-codoped ZnO is suggested to be due to the hybridization between delocalized holes and spin-split Cu 3d states.     

Ni含量对FeCoNiB软磁薄膜微波电磁性能的影响

为了改良磁性材料的高频电磁性能,采用射频磁控溅射工艺制备了一系列FeCoB和FeCoNiB磁性薄膜.研究了Ni元素的引入对材料微结构和电磁性能的影响.结果表明,适量的Ni添加量有利于获得优良的微波电磁性能,这主要归因于B在晶粒边界的析出.制备的厚度约为200nm薄膜样品在GHz频段下同时具有高饱和磁化强度47πMs=2...     

Correlation between hardness and stress in Al-(Nb, Mo, Ta) thin films

The thin films of Al_xNb_1 − x (95 ≥ x ≥ 20), Al_xMo_x (90 ≥ x ≥ 20) and Al_xTa_1 − x (95 ≥ x ≥ 20) were prepared by magnetron codeposition at room temperature. The average film thickness was from 325 to 400 nm, depending on the film composition. The structure of the as-deposited films was examined by the X-ray diffraction. The stress of the films was determined from the substrate deformation by the profilometer, and the microhardness (load 2 mN) was examined by the micro- and nano-hardness device. For the purpose of the examination of the hardness, the samples were deposited onto the sapphire wafers, while the examination of the film stress, was performed by using thin glass substrates. For all the Al-(Nb, Mo, Ta) alloy compositions, the microhardness is predominantly under the influence of the harder element, and monotonically decreases with the increase of the aluminum content. However, the microhardness of the amorphous AlTa films was higher than the bulk value of a harder element (Ta) in the alloy. A simple empirical linear relationship between the Vickers hardness, the bulk value hardness of the transition metal (harder element) and the elastic energy fraction of the identation deformation, was established. The elastic energy fraction in the microhardness is also linearly correlated with the stress in films.     

Characterization and dielectric properties of Ba5NdZnM9O30 (M=Nb, Ta) ceramics

Ba₅NdZnM₉O₃₀ (M=Nb, Ta) ceramics were prepared by the conventional high temperature solid state reaction route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy methods. They belong to paraelectric phases of filled tetragonal tungsten bronze structure at room temperature and have high dielectric constants of 282 and 85, combined with low dielectric losses of 0.0048 and 0.0081 at 1 MHz for Nb- and Ta-based ceramics, respectively.     

Magnetic properties and thermal stability of Co-TM-Zr (TM=Nb,Ta, Mo,W, and Ni) amorphous sputtered films for magnetic heads

The magnetic properties and thermal stability Co-TM-Zr (TM=Nb, Ta, Mo, W, and Ni) amorphous films prepared by rf diode sputtering are investigated. Amorphous films with a homogeneous structure and coercive force H _c of less than 20 A m^–1 are obtained at an argon gas pressure of 0.3–1 Pa. The formation range of the amorphous films is broad in the systems containing Ta and Nb, whereas it is limited to the composition range greater than 4–5 at % of Zr in the systems of Mo, W, and Ni. The magnetostriction _s depends on the concentration ratio of Zr and the TM. Films with zero _s are obtained at concentration ratios C _zr/C _TM ranging from 0.3 for Co-Nb-Zr films to 1.5–1.7 for Co-W-Zr films. The crystallization temperature T _x is highest in Co-Ta-Zr films and lowest in Co-Mo-Zr films when _s is zero and both films have the same saturation magnetic flux density B _s . The anisotropy field H _k is highest in Co-Ni-Zr films and lowest in Co-Nb-Zr films. These results indicate that Co-Ta-Zr and Co-Nb-Zr amorphous films are suitable for use as magnetic head materials because of the Co-Ta-Zr film's high T _x and B _s , and the Co-Nb-Zr film's small ns and low H _K      

Investigation of structural,optical and electrical properties of (Ti,Nb)Ox thin films deposited by high energy reactive magnetron sputtering

In this work the results of investigations of the titanium-niobium oxides thin films have been reported. The thin films were manufactured with the aid of a modified reactive magnetron sputtering process. The aim of the research was the analysis of structural, optical and electrical properties of the deposited thin films. Additionally, the influence of post-process annealing on the properties of studied coatings has been presented. The as-deposited coatings were amorphous, while annealing at 873 K caused a structural change to the mixture of TiO₂ anatase-rutile phases. The prepared thin films exhibited good transparency with transmission level of ca. 50 % and low resistivity varying from 2 Ωcm to 5×10^?2 Ωcm, depending on the time and temperature of annealing. What is worth to emphasize, the sign of Seebeck coefficient changed after the annealing process from the electron to hole type electrical conduction.     

High porosity and low thermal conductivity high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C

Porous ultra-high temperature ceramics (UHTCs) are promising for ultrahigh-temperature thermal insulation applications. However, the main limitations for their applications are the high thermal conductivity and densification of porous structure at high temperatures. In order to overcome these obstacles, herein, porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2 Ta_0.2)C was prepared by a simple method combing in-situ reaction and partial sintering. Porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C possesses homogeneous microstructure with grain size in the range of 100–500 nm and pore size in the range of 0.2–1 μm, which exhibits high porosity of 80.99%, high compressive strength of 3.45 MPa, low room temperature thermal conductivity of 0.39 W·m⁻¹ K⁻¹, low thermal diffusivity of 0.74 mm²·s⁻¹ and good high temperature stability. The combination of these properties renders porous high entropy (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C promising as light-weight ultrahigh temperature thermal insulation materials.     

Electrical properties of BaTi1−x M x O3 (M = Nb, Ta, Mo, W) ceramics

The electrical properties of BaTi_1?x M _x O₃ (M = Nb, Ta, Mo, W) ceramics (partial substitution of Group V (Nb, Ta) or VI (Mo, W) metals on the titanium site) have been studied by impedance spectroscopy. The results indicate that the Group VI metals (Mo and W) are less effective as donor dopants of barium titanate than are Nb and Ta because most of the Mo and W ions reside in the outer layer of the grains, raising its resistance.     

Fe-O纳米晶合金膜的软磁和高频特性

采用等离子体增强射频磁控溅射沉积方法,在室温下制备了Fe-O合金薄膜.研究了氧的掺杂量和薄膜厚度对薄膜软磁和高频特性的影响.结果发现少量氧的掺杂不导致低饱和磁化强度铁氧化物的形成,但可使薄膜晶粒细化,矫顽力下降.在薄膜厚度低于150 nm且氧气与氩气相对流量比为2.4%的条件下,薄膜的实部磁导率高达1100且能够维持到1GHz.     

The relaxation processes in the Al-(Nb,Mo, Ta,W) binary amorphous thin films

Structural relaxation and crystallization of Al-(Nb, Mo, Ta, W) amorphous thin films under isochronal condition were examined by continuous in situ electrical resistance measurements in vacuum. The amorphous Al-early transition metals (TE) thin films were prepared by simultaneous sputtering from two independently controlled DC magnetron sources in the CMS 18 deposition device. The structure of the as-deposited, heat-treated, and crystallized films was investigated by the XRD method. The dynamical crystallization temperature was estimated from the rapid change of the derivative of resistivity vs. temperature curve (dρ/dT). For the isochronal heating, it was observed that the relaxation effects decreased with an increase of the heating rate and decreased with the content of early transition metal in the film. Assuming the linear dependence of resistivity with temperature (Δρ/ρ_RT = αΔT) in the observed temperature interval the linear ρ(T) dependence is extracted from the relaxation effects. Adopted experimental function of ρ(T) is fitted to a modified Bloch–Grüneisen formula. Excellent agreement of experimental data and fitting function is obtained.     

Formation of complex alkoxides to control layer structure in Sr-Bi-M-O (M: Ta or Nb) perovskite thin films

Precursors for layer-structured perovskite thin films of Sr₂Bi₂Ta₃O_12.5 or SBT223, and Sr₂Bi₂Nb₃O_12.5 or SBN223 were prepared by the reactions of Sr-Bi (2 : 2) double methoxyethoxide and Ta or Nb methoxyethoxide, followed by partial hydrolysis. By several analytical techniques, such as ¹H-, ¹³C- and ⁹³Nb-NMR (nuclear magnetic resonance) and FT-IR (Fourier transform infrared) the molecular structure of the precursors was found to be similar to the layer-structured perovskite crystal sub-lattice. As a result, the onset of crystallization in the sol-gel derived SBT223 thin films was at a low temperature of 550°C. By rapid thermal annealing in an oxygen atmosphere, the single-phase perovskite films exhibited preferred (1 1 7) orientation. In contrast to the SBT system, the observed number of the pseudo-perovskite layers of TaO₆ octahedral units between Bi₂O ₂ ^{2 +} layers in the SBT223 was three. Despite the elongation of the unit cell along the c-axis, 700°C-heated SBT223 thin film did not exhibit a saturated hysteresis loop due to the small crystallite size.     

富氮MeNx(Me=Ti,Zr,Hf)薄膜的结构与红外光学性能

用射频反应磁控溅射方法制备了MeNx(Me=Ti、Zr、Hf)薄膜,研究了在富N2条件下不同的N2/Ar流量比对薄膜结构和光学性能的影响.掠角X射线衍射的分析结果表明,所制得的富氮的TiNx薄膜主要由TiN所组成,而富氮的ZrNx、HfNx薄膜则具有非晶态的结构.用分光光度计和傅里叶红外仪对薄膜的光学透过率的测试表明,...     

Sputter alloying of Ni,Ti and Hf for fabrication of high temperature shape memory thin films

Abstract

In the present paper, the fabrication and characterisation of typical high temperature Ni(Ti+Hf) alloyed thin films produced by simultaneous sputter deposition from separate elemental Ni, Ti and Hf targets are presented. Film composition, determined by energy dispersive X-ray spectroscopy, was controlled by adjusting the ratio of powers applied to each target. Films deposited at room temperature had an amorphous structure and subsequent annealing at 550°C was carried out in a high vacuum environment, based on crystallisation temperature evaluation by differential scanning calorimetry (DSC). High temperature martensitic transformation, confirmed by DSC and variable temperature X-ray diffraction (XRD), was achieved by deposition of (Ti+Hf) rich Ni–Ti–Hf films. Any slight change of composition towards Ni rich reduced the transformation temperature. Atomic force microscopy and XRD illustrated that the films had a fine grain structure (～100 nm). One way shape memory effect was observed at ～200°C in a film with composition of 15·6 at.-%Hf.     

Magnetic properties and high frequency characteristics of isotropic FeCoZr thin films with stripe domains

Magnetic properties and high frequency characteristics of (Fe_70.6Co_29.4)_100?xZr_x (x?=?4.0???18.2 at.%) thin films have been investigated. The saturation magnetization 4πM _s decreases continuously from 21.7 kGs for x?=?4.0 at.% to 12.2 kGs for x?=?18.2 at.% and it is consistent with the decreasing of Fe-Co composition. It is found that the films show nearly isotropic magnetic behavior in the film plane for the Zr content ranging from 7.2 to 18.2 at.%. These films exhibit a weak perpendicular magnetic anisotropy with coercivity values of 24–67 Oe. Meanwhile, the in-plane isotropic FeCoZr films show a good high frequency response of permeability. In particular, the film with x?=?7.2 at.% shows a resonance frequency of 2.8 GHz along the direction perpendicular to the stripe domain axis. The permeability spectra of the thin films with higher Zr content display multiple resonance peaks, which may be due to the perpendicular magnetic anisotropy induced by the stress.     

Electrical characteristics of the MOD-derived SrBi2xTa2O9 and SrBi2.4(Ta,Nb)2O9 thin films

Ferroelectric and leakage current characteristics of the MOD-derived SrBi_2xTa₂O₉ (0.8 x 1.6) and SrBi_2.4(Ta_1-yNb_y)₂ O₉ (0 y 1) thin films were investigated. The SBT and SBTN films were fully crystallized to Bi-layered perovskite structure by annealing at 800°C for 1 hour in oxygen atmosphere. The ferroelectric characteristics of the SBT films were optimized at the Bi/Ta mole ratio x of 1.2. The leakage current density of the Bi-excess SBT films decreased remarkably by the post-metallization annealing at 800°C for 10 minutes in oxygen ambient. The ferroelectric characteristics of the SBTN films were optimized with the SBN content y of 0.25. The SrBi_2.4(Ta_0.75Nb_0.25)₂ O₉ film exhibited 2P_r and E_c of 19.04 C/cm² and 24.94 kV/cm at ±5 V, which were superior to 2P_r of 11.3 C/cm² and E_c of 39.6 kV/cm obtained for the SrBi_2.4Ta₂O₉ film after the post-metallization annealing. The MOD-derived SrBi_2.4(Ta_0.75Nb_0.25)₂O₉ film did not exhibit the polarization fatigue after 10¹¹ switching cycles at ±5 V.     

Ambient temperature formation of (Ta,Nb)C and (Ta,Nb)N

A tantalum/niobium concentrate has been mechanically milled with magnesium and either graphite or nitrogen for 100 h. Directly after milling the formation of MgO was evident in both systems, a mixed metal carbide (Ta,Nb)C was also present in the carbon system. A cubic phase, close to that expected for the mixed metal nitride, was found in the powder milled under nitrogen. Annealing of the powders showed the reaction was incomplete with reduced oxide phases present. The carbide/nitride phases were readily separated from the MgO by acid leaching which left powders <5 m in size. The leaching preferentially dissolved the smaller, more highly strained crystallites in both cases.