BaTiO3 PTCR陶瓷阻温系数的研究

本文以Ｈｅｙｗａｎｇ模型为基础，分析了影响ＢａＴｉＯ３ＰＴＣＲ陶瓷阻温系数α的主要因素，并给出了解析关系，各参数的测量结果与该关系基本相符。     

TiO2对Y掺杂PTCR陶瓷材料性能的影响

本文对ＴｉＯ２原料的晶型、颗粒状况和纯度对Ｙ＾３＋掺杂ＢａＴｉＯ３基ＰＴＣＲ材料的显微结构、电性能的影响作了探讨，结果表明，ＴｉＯ２原料的晶型、颗粒大小和团聚状况都将影响到ＰＴＣＲ陶瓷的显微结构，ＴｉＯ２原料的晶型对ＰＴＣＲ陶瓷半导化过程有影响，原料存在杂质和团聚，将使ＰＴＣＲ陶瓷的电阻－温度特性变差。     

LDPE／炭黑复合导电材料PTC／NTC效应形成机理的探讨

本文从ＬＤＰＥ／炭黑复合导电材料的结晶性能出发，探讨了复合材料电阻率的正温度系数效应和负温度系数效应的形成机理，认为ＰＴＣ效应是由聚合物熔融时发生的晶相向非晶相的转变以及由此而产生的热膨胀共同引起，ＮＴＣ效应主要与炭黑粒子的附聚效应有关。     

程控电话交换机过电流保护用PTC陶瓷材料的制备

程控电话交换机过电流保护元件要求用低电阻率高性能的ＰＴＣ陶瓷材料来制备．本文叙述了在（Ｂａ－Ｓｒ－Ｐｂ）ＴｉＯ３固溶体为基的化学组成中，通过对原材料特性的控制、多种添加物改性以及特定的烧成工艺等手段，获得了居里温度为９０°Ｃ、室温体积电阻率为３０Ω．ｃｍ和电阻率随温度的变化幅度超过１０５的ＰＴＣ陶瓷材料，并成功地制得了用于程控电话交换机过电流保护元件．     

Mn掺杂BaTiO_3基PTCR陶瓷相变的EPR研究

为了探索利用ＥＰＲ谱线对ＰＴＣＲ陶瓷的相变及ＰＴＣ效应的机制研究的可能性,本文对接 Ｍｎ的 ＢａＴｉＯ３基正温度系数热敏电阻（简称ＰＴＣＲ）陶瓷在 １２０～４５０Ｋ温度范围内的电子顺磁共振谱进行了研究．得出了 Ｍｎ２＋离子 ＥＰＲ信号强度、 ｇ因子值和超精细耦合常数｜Ａ｜值的温度分布,发现ＥＰＲ参数与ＰＴＣＲ陶瓷相变有明显的对应关系,并给出微观结构上的初步解释．研究表明ＥＰＲ谱线以及精细结构的分析可以为ＰＴＣＲ陶瓷的相变机制以及ＰＴＣ效应的机制研究提供新的途径．     

温度对高密度聚乙烯－炭黑材料电性能的影响

讨论了ＨＤＰＥ－ＣＢＰＴＣ导电材料的电性能与温度的关系，发现在一定温度范围内，Ｒ－Ｔ关系符合Ｒ＝Ｒ·ｅｘｐ（αＴ），α为材料电阻随温度变化的温度系数，α值受聚合物基材的影响，ＣＢ含量及热处理不改变α的值，但可改ＩｎＲ－Ｔ成线性关系的温度范围，随着温度升高，表征材料导电性质的Ｂ值并非全都升高。对热－冷循环过程中ＰＥ－ＣＢ材料的Ｒ－Ｔ关系的研究表明：升温曲线与冷却曲线存在不同程度的偏离，热处理及交联处理可减小这种偏离，交联可以有效地消除ＰＴＣ材料的ＮＴＣ现象。     

相变扩张对低阻值PTC材料阻温特性的影响

本文研究了载流子迁移率和相变扩张对低阻值ＰＴＣ材料阻温特性的影响，指出常温电阻率很低（２５Ω，ｃｍ左右）的ＢａＴｉＯ＿３ＰＴＣ材料的阻温关系中产生反常规象的原因，是施主电离能较低以及材料的相变扩张。同时，常温电阻率很低的ＰＴＣ材料，其升阻比也难以做得较高。     

Ni-Cr-P三元合金化学镀层的组织结构

用ＳＥＭ ，ＴＥＭ ，ＤＴＡ，ＸＲＤ 等方法研究了化学镀Ｎｉ－Ｃｒ－Ｐ 三元合金镀层的形貌和结构变化。结果表明，镀层组成均匀，呈非晶态结构，初始晶化温度为２７０．７ ℃，热处理可使镀层析出晶态Ｎｉ相和 Ｎｉ３Ｐ 相，高温热处理条件下还有晶态Ｃｒ 相和 Ｃｒ３Ｐ 相析出。     

金属—PTC陶瓷复合材料制备工艺及机理的研究

金属－ＰＴＣ陶瓷复合材料是电子功能型的陶瓷基复合材料。本文介绍了Ｆｅ、Ｃｏ、Ｎｉ－ＰＴＣ陶瓷复合材料的制备方法，测定了材料的阻温特性，讨论了样品的ＮＴＣ现象及阻温特性机理。     

YF3掺杂钛酸钡半导体材料特性研究

在不同气氛下制备了ＹＦ３掺杂钛酸钡材料,并对其电阻的正温度系数特性进行了研究。借助于ＸＲＤ、ＳＥＭ、ＸＲＦ、阻温特性测试仪和阻抗分析仪,研究了不同处理气氛对ＹＦ３掺杂肽到钡材料结构和性能的影响。研究结果表明,在空气和在氩气中烧结的ＹＦ３掺杂钛酸钡材料都是Ｎ型半导体,其中Ｙ取代Ａ位,Ｆ取代Ｏ位,并对在氢气氛中烧结的ＹＦ３掺杂钛酸钡材料还观察到了不同的ＰＴＣＲ效应。这种ＰＴＣＲ效应的产生可能是由于存在新的取代机制－－Ｏ位取代的半导化机制引起的。     

BaTiO3-based positive temperature coefficient of resistivity ceramics with low resistivities prepared by the oxalate method

Positive temperature coefficient of resistivity (PTCR) ceramics with low resistivities at room temperature were obtained by using oxalate-derived barium titanate powders. The average room-temperature resistivity of the PTCR ceramics was 4 cm, and the magnitude of their PTCR jump was around four orders with a voltage proof of more than 50 Vmm^–1. These PTCR properties are significantly influenced by the calcination temperature of the starting materials and by the resultant properties of the ceramic bodies. The microstructure of such-PTCR ceramics with a low room-temperature resistivity produced in this study was found to be rather heterogeneous. Complex impedance measurements revealed that the resistivity of the present PTCR materials was determined predominantly by the grain-boundary resistance even at room temperature.     

The positive temperature coefficient of resistivity in barium titanate

Positive temperature coefficient of resistivity (PTCR) materials have become very important components, and among these materials barium titanate compounds make up the most important group. When properly processed these compounds show a high PTCR at the Curie temperature (the transition temperature from the ferroelectric tetragonal phase to the paraelectric cube phase). In the first half of this paper literature related to the resistivity-temperature behaviour is discussed. As explained by the well established Heywang model, the PTCR effect is caused by trapped electrons at the grain boundaries. From reviewing experimental results in the literature it is clear that the PTCR effect can not be explained by assuming only one kind of electron trap. It is concluded that as well as barium vacancies, adsorbed oxygen as 3d-elements can act as electron traps. In the second half of this paper, the influence of the processing parameters on the PTCR related properties is discussed. Special emphasis is placed on the phenomenon that the conductivity and grain size decrease abruptly with increasing donor concentration above ∼ 0.3 at%. Several models explaining this phenomenon are discussed and apparent discrepancies in experimental data are explained.     

Studies on the preparation of positive, temperature coefficient of resistivity powder by two chemical steps

Ultrafine and homogeneous positive temperature coefficient of resistivity (PTCR) powder was prepared by two chemical steps: citrate and liquid-phase coating process. The physical and chemical properties of the powder were investigated in detail. The dimensions of the primary particles in the PTCR powders were about 20–50 nm. Sintering aids and acceptors could be distributed homogeneously in doped BaTiO3 powder through the liquid-phase coating process. Sintered from this powder produced samples with excellent PTCR effects (ΔR=106, ΔT=110°C, α30=26%°C-1). This revised version was published online in November 2006 with corrections to the Cover Date.     

炭黑填充导电橡胶的温度传感器灵敏系数

以通用有效介质理论为基础,给出了炭黑填充导电橡胶(导电炭黑/橡胶)的温度传感器电阻-温度计算模型。利用该模型得出材料的灵敏系数计算公式,并结合形变和电阻率的变化对正电阻-温度特性(PTCR)的影响分析材料的灵敏系数特性。结果表明:在炭黑分布均匀、体积分数在渗流体积分数附近等条件下,电阻-温度计算模型与实验吻合,表现出一致的PTCR变化规律。导电炭黑/橡胶的PTCR效应主要源于基体膨胀导致炭黑体积分数的稀释作用,若炭黑体积分数在渗流区,导电炭黑/橡胶的灵敏系数为280~420;当炭黑体积分数在传导区时,其灵敏系数为32.5~62.0。导电炭黑/橡胶的PTCR效应是热-形变与形变-电导过程的乘积效应,导电炭黑/橡胶的灵敏系数高,但其体积膨胀系数低,使材料的电阻温度系数较低。     

无铅BaTiO_3系热敏电阻及其PTC性能的研究进展

通常在BaTiO3中固溶PbTiO3来提高BaTiO3系PTCR的居里温度,但是铅的毒性和挥发性限制了BaTiO3系PTCR的应用,因此需要研制出高居里点的无铅PTCR陶瓷。随着BNT、BKT含量增加,BaTiO3系PT-CR的居里点升高,但同时室温电阻快速增大。若在提高居里点的同时抑制室温电阻率的增大,就能制备出有实用价值的无铅高居里点的PTC材料。综述了BNT、BKT的含量对居里温度的影响及其机理,通过加入还原剂或在还原气氛下烧结并制定合理的烧结制度可以得到低室温电阻率和性能较好的PTC材料。     

基于炭黑填充导电橡胶的压力/温度传感器非线性特性

通过研究电阻率和电阻几何系数对"负电阻-压力系数"(NPCR)和"正电阻-温度系数"(PTCR)的影响,分析了炭黑填充导电橡胶(导电炭黑/橡胶)的压力/温度传感器的非线性特性。结果表明: 导电炭黑/橡胶的NPCR和PTCR效应产生非线性的主要原因为电阻率的非线性变化; 当炭黑体积分数接近渗流体积分数时,其电阻率对体积的变化敏感程度高,此时,导电炭黑/橡胶的NPCR和PTCR效应的非线性特性较强; 由于导电炭黑/橡胶的体压缩系数大于其热膨胀系数,且导电炭黑/橡胶在压力场和温度场下的形变过程不同,导电炭黑/橡胶NPCR效应的非线性强于PTCR效应的非线性。     

PTCR property in carbon-NaCl composites

The composition dependence of resistivity and the positive temperature coefficient of resistivity (PTCR) were investigated in composites of electrically conducting carbon and insulating NaCl. Resistivity at 20C of the composites decreased rapidly with increasing carbon volume fraction above a critical volume fraction, V_c, which was well expressed by an equation of the percolation theory. The value of V_c decreased from 25 vol% to 4 vol% when the particle size ratio of NaCl/carbon increased from 0.5 to 50. When the carbon volume fraction was close to the value of V_c, the composites showed pronounced PTCR properties with a resistivity increase of five orders of magnitude and a temperature coefficient of 15%–17% K^–1. A composite of all inorganic materials with a controllable PTCR property is suggested to be possible.     

Positive temperature coefficient of resistance effects in BaPbO3/polyethylene composites

The positive temperature coefficient of resistance (PTCR) properties of BaPbO₃/polyethylene composites have been investigated as a function of the volume ratio of BaPbO₃ to polyethylene. The PTCR effect increased up to nine orders of magnitude greater than that of semiconducting BaTiO₃ ceramics. However, the PTCR effect decreased with increasing BaPbO₃ content. The PTCR effect was dependent on the tunnelling current in the BaPbO₃ intergrain gap. When the PTCR effect was measured repeatedly, the resistivity at room temperature increased, the PTCR effect decreased, and the transition temperature shifted to a lower value. These results could be explained by the thermal properties of polyethylene and the large structural change of composites in the repeated measurements.     

Effect of atmosphere on the PTCR properties of BaTiO3 ceramics

The influence of low-temperature annealing, at < 360 °C, in various reducing and oxidizing atmospheres for a series of BaTiO₃ ceramics with a positive temperature coefficient of resistance (PTCR) is discussed. Combined impedance and modulus spectroscopy is used to analyse a.c. impedance data and shows that the total resistance of the sample can be composed of up to three components, dependent on the cooling rate from the sintering temperature. For quickly cooled samples the PTCR response is dominated by an outer shell on individuals grains, whereas for slowly cooled samples the grain boundary resistance dominates. Annealing in reducing atmospheres destroys the grain boundary PTCR effect whereas the outer-shell grain PTCR effect is relatively insensitive to the reducing atmosphere. It is proposed that the acceptor states responsible for the outer-grain and grain-boundary PTCR effects are predominantly intrinsic metal vacancies, i.e. Ba and/or Ti, and adsorbed oxygen, respectively.