Ba_xNi_(1–x)La_yFe_(12–y)O_(19)铁氧体的制备与磁性能研究

首先利用溶胶-凝胶法制备了BaxNi1–xFe12O19(x=0.2,0.4,0.6,0.8)样品,通过热重-差示扫描量热仪(TG-DSC)、X射线衍射仪(XRD)和振动试样磁强计(VSM)分析,确定了最佳煅烧温度和最佳Ba-Ni摩尔比。然后利用同样的方法制备了Ba0.6Ni0.4LayFe12–yO19(y=0,0.1,0.3,0.5)样品,利用场发射扫描电镜(FESEM)、XRD和VSM对产物进行表征分析。结果表明Ni2+取代Ba2+,进入其晶格内部,改变了铁氧体的磁性能。La3+的加入改变了铁氧体的矫顽力Hc、饱和磁化强度Ms和剩余磁化强度Mr。当y=0.3时,其Ms和Mr达到最大值,分别为51.0 A.m2/kg和32.3 A·m2/kg。     

退火温度对La_(1–x)Sr_xCo_(1–y)Fe_yO_3系薄膜NTC阻温特性的影响

利用La_(1–x)Sr_xCo_(1–y)Fe_yO_3(x=0.2,y=0.3)陶瓷靶材,通过真空射频磁控溅射在Al_2O_3基片上制备La_(0.8)Sr_(0.2)Co_(0.7)Fe_(0.3)O_3(LSCF)薄膜,然后在此基础上制备NTC热敏电阻。采用X射线衍射(XRD)分析了材料相的组成,扫描电子显微镜(SEM)分析观察薄膜材料的微观结构,电阻测试仪和四探针仪器测试薄膜的阻温特性,研究不同退火温度对LSCF薄膜室温电阻和材料常数(B值)的影响。结果表明,随着退火温度升高,LSCF薄膜方阻和B值都存在先减小后增大现象,具有显著的NTC阻温特性,其lnR-T~(–1)曲线具有良好的线性度。     

Co含量对Ni_(0.9–0.5x)Co_(0.3+1.5x)Mn_(1.8–x)O_4热敏电阻性能的影响

采用传统的固相反应法制备了Ni0.9–0.5xCo0.3+1.5xMn1.8–xO4(Mn和Ni的摩尔比为2:1,x=0~0.7)陶瓷。并且采用XRD和SEM等手段,系统地分析了Co含量对该热敏陶瓷的相结构及显微形貌的影响。结果表明,所研究的陶瓷均为立方晶相,当x≥0.6时出现第二相CoO岩盐相。在–40~125℃的测试范围内,该陶瓷材料表现出明显的NTC特性。随着Co含量的增加,陶瓷的室温电阻率(2 275~914?·cm)及β值(3 718~3 544 K)均逐渐减小,并且出现两个拐点。其导电机理与小极化子的跳跃电导模型相吻合,并且受CoO岩盐相的影响。     

Properties of epitaxial (Al x Ga1 − x As)1 − y C y alloys grown by MOCVD autoepitaxy

The growth of epitaxial Al _x Ga_{1 ? x} As:C alloys by metal-organic chemical vapor deposition (MOCVD) at low temperatures results in the formation of quaternary (Al _x Ga_{1 ? x} As)_{1 ? y} C _y alloys, in which carbon atoms can be concentrated at lattice defects in the epitaxial alloy with the formation of impurity nanoclusters.     

Synthesis of compositionally different multicomponent metal-oxide films (SnO2) x (ZnO)1 − x (x = 1–0.5)

The study is concerned with high-purity SnO₂ and ZnO powders produced from salt solutions of corresponding metals by low-temperature hydrothermal synthesis. Fragments of SnO₂ and ZnO ceramic targets formed as 1 × 8 cm bars are fabricated by dry pressing. The bars are used to form composite targets for ion-beam sputtering and the fabrication of compositionally different (SnO₂) _x (ZnO)_{1 ? x} (x = 1–0.5) films appropriate for the production of gas sensors or transparent electronic devices. The optical and electrical parameters of the films with different compositions are studied.     

On the preparation and photoelectric properties of Tl1–x In1–x Sn x Se2 (x = 0.1–0.25) alloys

The technological conditions for growing single crystals of Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.     

溶胶–凝胶法制备 Pb(Zrx, Ti1–x)O3 薄膜研究进展

Pb(Zrx, Ti1-x) (PZT)铁电薄膜因具有优良的铁电性、压电性、热释电性和声光性能而受到广泛关注,其电、光性能与其制备过程密切相关。简要介绍了 PZT 薄膜制备工艺流程,系统地从前驱体溶液、摩尔比 r(Zr:Ti)、热处理工艺、电极材料以及掺杂改性等五个方面概述了 sol-gel 法制备 PZT 薄膜的研究进展,并指出了目前 sol-gel 法制备 PZT 铁电薄膜研究中存在的一些问题以及未来的研究方向。     

Effect of Surface Preparation on Mechanical Properties of Ni Contacts on Polycrystalline (Bi1?x Sb x )2(Te1?y Se y )3 Alloys

We present a comparison of different surface preparation techniques for hot-extruded (Bi_1?x Sb _x )₂(Te_1?y Se _y )₃ alloys prior to Ni plating and their consequences on adhesion. The surface preparation is carried out by a relatively fast and well-controlled electrochemical etching procedure that provides morphologies with homogeneous flat surfaces on a scale of tens of micrometers. This procedure is not optimal for Ni metallization since it does not ensure enough roughness on the surface. Applying wet chemical etching with hypochlorite and nitric acid after the electrochemical etching changes the morphology, and the surface roughness increases, as evidenced by scanning electron microscopy and atomic force microscopy. Tensile tests carried out on n-type and p-type 1-mm-thick specimens, covered with a 12-??m Ni layer followed by Sn-Pb soldered joints, confirm a significant improvement in the ultimate adhesion strength, with fracture occurring within the thermoelectric material. Use of this two-step surface treatment, after slicing and prior to metallization, leads to maximum adhesion strength of around 38?MPa for either type of thermoelectric material. These results are consistent with the morphological changes observed by scanning electron microscopy on the surface after chemical etching.     

Electrochemical Deposition and Characterization of Thermoelectric Ternary (Bi x Sb1?x )2Te3 and Bi2(Te1?y Se y )3 Thin Films

Thermoelectric thin films of the ternary compounds (Bi _x Sb_1?x )₂Te₃ and Bi₂(Te_1?y Se _y )₃ were synthesized using potentiostatic electrochemical deposition on gold-coated silicon substrates from aqueous acidic solutions at room temperature. The surface morphology, elemental composition, and crystal structure of the deposited films were studied and correlated with preparation conditions. The thermoelectric properties of (Bi _x Sb_1?x )₂Te₃ and Bi₂(Te_1?y Se _y )₃ films, i.e., Seebeck coefficient and electrical resistivity, were measured after transferring the films to a nonconductive epoxy support. (Bi _x Sb_1?x )₂Te₃ thin films showed p-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively large negative potential with composition close to Bi_0.5Sb_1.5Te₃. In addition, Bi₂(Te_1?y Se _y )₃ thin films showed n-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively small negative potential, having composition close to Bi₂Te_2.7Se_0.3. In contrast to Bi₂Te_2.7Se_0.3 thin films, an annealing treatment was required for Bi_0.5Sb_1.5Te₃ thin films to achieve the same magnitude of power factor as Bi₂Te_2.7Se_0.3. Therefore, Bi₂Te_2.7Se_0.3 thin films appear to be good candidates for multilayer preparation using electrochemical deposition, but the morphology of the films must be further improved.     

Structural and spectral features of MOCVD Al x Ga y In1 ? x ? y As z P1 ? z /GaAs (100) alloys

The study is concerned with MOCVD epitaxial heterostructures grown on the basis of Al _x Ga _y In_{1 ? x ? y} As _z P_{1 ? z} quinary alloys in the region of alloy compositions isoperiodic to GaAs. By the X-ray diffraction technique and atomic force microscopy, it is shown that, on the surface of the heterostructures, there are nanometric objects capable of lining up along a certain direction. From calculations of the crystal lattice parameters with consideration for internal strains, it can be inferred that the new compound is a phase based on the Al _x Ga _y In_{1 ? x ? y} As _z P_{1 ? z} alloy.     

一种快速简便测定单轴晶体x(y)轴及半波电压的方法

KDP,DKDP等单轴晶体在激光技术中通常被作为激光器的Q开关使用,在实际应用中,晶体的x(y)轴及其半波电压的标定为激光器的调试带来很大方便,我们介绍一种快速简便测定单轴晶体x(y)轴及其半波电压的方法。     

Structure and optical properties of heterostructures based on MOCVD (Al x Ga1 − x As1 − y P y )1 − z Si z alloys

Epitaxial heterostructures produced by MOCVD on the basis of Al _x Ga_{1 ? x} As ternary alloys with the composition parameter x ≈ 0.20–0.50 and doped to a high Si and P atomic content are studied. Using the high-resolution X-ray diffraction technique, scanning electron microscopy, X-ray microanalysis, Raman spectroscopy, and photoluminescence spectroscopy, it is shown that the epitaxial films grown by MOCVD are formed of five-component (Al _x Ga_{1 ? x} As_{1 ? y} P _y )_{1 ? z} Si _z alloys.     

(Mg_(1–x)Zn_x)TiO_3系陶瓷微波介电性能的研究

以MgCO3、ZnO和TiO2为原料,用固相反应法制备了(Mg1–xZnx)TiO3(MZT)系陶瓷。研究了ZnO含量对其微观结构和微波介电性能的影响。结果表明:添加适量ZnO,可有效降低烧结温度,拓宽烧结温度范围。当x(ZnO)为30%,烧结温度为1250℃时,MZT陶瓷具有优良微波介电性能,εr为16～18,Q·f为90000GHz,τc为–5.1×10–7℃–1。     

Piezo displacement sensors for a compact high-speed x–y nanopositioner in differential actuation mode

An emerging actuation technique in piezo driven nanopositioners is differential actuation, where each axis has two opposing actuators that operate differentially and provide bilateral motion. It has simultaneous benefits of improving linearity and range of displacement. However, few methods for displacement sensing employing in-situ transducers have been considered for this kind of nanopositioners. We address a novel application of PZT piezoelectric chips for direct displacement sensing in differentially driven nanopositioners. First, an electromechanical force analysis is performed in order to increase the PZT sensor sensitivity through the structural design of the nanopositioner. Secondly, the sensing performances of the proposed in-situ PZT sensor are compared with those from an alternative built-in piezoresistive (PZR) strain gauge sensor under equal circumstances, in different sensing and actuation configurations. While the PZR sensor has a larger sensing bandwidth than the PZT one and performs better if the actuation frequency is smaller than 30 Hz, the PZT sensors provides better accuracy when the actuation is well within its sensing bandwidth. The accuracy of the differential sensors and the input-displacement linearity are improved when the mechanical preload force magnitudes on the opposing actuators are balanced. The differential PZT sensor can provide accurate measurements even in a non-differential mode after recalibration.     

Vanadium deep impurity level in diluted magnetic semiconductors Pb1 ? x ? y Sn x V y Te

The crystal structure, Sn and V distribution over the length of single-crystal ingots, and galvanomagnetic effects in low magnetic fields (4.2 K ?? T ?? 300 K, B ?? 0.07 T) in Pb_1?x?y Sn _x V _y Te alloys (x = 0.05?0.21, y ?? 0.015) are studied. It is shown that all the samples are single-phase, while the Sn and V concentrations exponentially increase from the beginning to the end of the ingots. Upon doping with V, a decrease in the concentration of free holes and a metal-insulator transition are found. They are related to the appearance of a deep impurity level of V in the band gap, electron redistribution between the level and the valence band, and pinning of the Fermi-level to the impurity level. The shift rate of the V level relative to the conduction band bottom is determined and a diagram of the reconstruction of the electronic structure of the Pb_{1 ? x ? y} Sn _x V _y Te alloy upon varying the host composition is suggested.     

Thermoelectric Properties of Light-Element-Containing Zintl Compounds CaZn2−x Cu x P2 and CaMnZn1−x Cu x P2 (x = 0.0–0.2)

Light-element-containing CaAl₂Si₂-type Zintl phases CaZn_2?x Cu _x P₂ and CaMnZn_1?x Cu _x P₂ (x = 0.0–0.2) have been synthesized by solid-state reaction. Electrical resistivity (ρ), Seebeck coefficient (α), and thermal conductivity (κ) were measured over a wide temperature (T) range (80–1000 K) to evaluate the thermoelectric potential of these materials. Below 300 K, the power factor (PF; α ²/ρ) is very small. Above 600 K, however, PF increases rapidly for all compositions because of a rapid increase of α and a simultaneous decrease of ρ. The measured large α is consistent with the wider band gap expected for these compositions. Compared with the pure compounds, larger PF values are observed for the Cu-substituted compounds; the largest observed PF is ～0.5 mW/m K². The thermal conductivity is found to be rather low, despite the presence of light elements, and is in the range 1.0–1.5 W/m K at 1000 K. Because of the combination of low κ and moderate PF values, the dimensionless figure of merit ZT = α ² T/ρκ reaches a maximum of 0.4 for CaZn_1.9Cu_0.1P₂.     

新型电接触材料Ag/La_(1–x)Sr_xCoO_3

回顾了电接触材料的发展历史并介绍了新型电接触材料Ag/La1–xSrxCoO3。分析了Ag/La1–xSrxCoO3电接触材料的性能特点,并指出当前研究中需要解决的关键问题:陶瓷成分及微观结构和复合材料成型工艺对材料最终性能的影响。最后阐述Ag/La1–xSrxCoO3材料可作为电接触材料的一个崭新发展方向。     

(Sr_(0.5)Ba_(0.5))_(1.9)Ca_(0.1)NaNb_(5–x)TaxO_(15)陶瓷的介电性能

通过Ta掺杂改性钨青铜陶瓷(Sr0.5Ba0.5)1.9Ca0.1NaNb5–xTaxO15(x=0～0.30),分析了Ta掺杂量对其烧结性能、微观结构及介电性能的影响。陶瓷的烧结温度随x的增大略有提高。当x<0.10时,陶瓷的tC和弛豫性变化不大;当x≥0.10时,tm(1kHz)明显降低,从270℃(x=0)降低至231℃(x=0.30)。且tm随频率增加向高温移动,弛豫性明显增强。认为Ta掺杂引起其性能变化是由于Ta—O键与Nb—O键键能的差异,导致陶瓷氧八面体中心离子位移量以及A位离子有序程度的变化所致。     

Thermoelectric Properties of Yb1−x (Er,Lu) x Al3 Solid Solutions

Ytterbium trialuminide (YbAl₃) has one of the largest thermoelectric power factors of known materials below room temperature, making it a material of interest for low-temperature thermoelectric devices. However, the high thermal conductivity, which is due to a combination of a large electronic thermal conductivity and a moderately large lattice thermal conductivity, is detrimental to the figure of merit. Substitution of different atoms on the Yb site was performed in order to assess their ability to favorably alter the electronic structure and/or reduce the lattice thermal conductivity. We have synthesized and studied the thermoelectric properties of the solid solutions of YbAl₃ with ErAl₃ and LuAl₃. Results for electrical conductivity, thermal conductivity, and Seebeck coefficient for several of these solid solutions over the temperature range of 80 K to 300 K are reported. Although most substituted samples are driven toward a metallic state, we find that for some compositions the figure of merit is enhanced relative to pure YbAl₃.