TS单晶非公度相变的研究

测量了 TS 单晶从77～300K 的介电常数和热膨胀系数,结果表明 TS 在发生非公度相变时介电常数和热膨胀系数均有反常,说明在相变过程中不仅侧链极性基团的取向发生变化,同时还存在原子的位移.     

PTS单晶的低频介电常数

测量了一维聚合物PTS单晶从77—273K沿分子链方向的低频介电常数,发现在相变温度附近,介电常数存在尖锐的峰值,与反铁电相变类似。     

TS单晶非公度相变膨胀系数的研究

本文研究了 TS 从77K 到300K 膨胀系数与温度的关系,结果表明 TS 在非公度相变时膨胀系数出现明显反常.分析了 TS、PTS 的结构,指出侧链极性基团的运动在其中起重要作用.与铁磁性、反铁磁性材料类比,说明了反铁电性对膨胀系数的影响.     

PTS单晶的介电性质

测量了一维聚合物PTS单晶从77K到273K沿分子链方向的介电性质。由介电常数的反常观察到在195K发生二级相变,从高温的非极性态转变为低温的极性态。发现介电损耗在150K和100K有两个峰。用侧链分子的三种运动方式解释了上述结果。 关键词：     

从变压器油溶液中提纯聚异丁烯

聚异丁烯是一种高分子物质,系由异丁烯经聚合而成。聚合度低的是无色粘稠液体,聚合度高的为橡胶状固体。在常温下,聚异丁烯的化学稳定性很好,光学辅料中常应用聚合度低的聚异丁烯作为密封、润滑材料的添加剂,借以改进产品的耐热、抗寒、耐水、耐酸等性能。在某些特殊的用途中,还可借以改善产品的电绝缘性能。聚异丁烯是碳链线型结构的高分子聚合物,它的结构式为: 由结构决定了它的性质,它易溶解于石     

阻挡层电容对ACu3Ti4O12巨介电性能的影响研究

用固相反应法成功地制备了ACu3Ti4O12(A=Ca,La,Y)系列陶瓷,在50-300K温区内测量了样品的介电性能,分析了交流电导与外场频率、温度的关系.发现在相同组分的CaCu3Ti4O12晶体中相对含量大于等于0.776时,样品的相对介电常数可达104;而A位上价态为3+的化合物La2/3Cu3Ti4O12和Y2/3Cu3Ti4O12相对介电常数仅为103.分析表明,样品中内部阻挡层电容数目的多少直接对ACu3Ti4O12的相对介电常数产生影响.电导与温度及频率的关系是由电子、声子与外场的共同作用决定的.     

PTS单晶的低温热膨胀系数

本文用电容法测量了PTS单晶从77—273K平行于分子链方向和垂直于分子链方向的热膨胀系数,实验观察到沿链方向的热膨胀系数在195K附近有突变,在200K附近出现负值。对此,我们作了定性的讨论。 关键词：     

Zn掺杂La2CuO4热电势和磁化率研究

测量了La2CuO4掺Zn样品在不同降温速率下(330K保温05h,然后分别以6Kh,02Ks的速度降到8K)的直流磁化率和热电势.实验结果表明,反铁磁温度TN不随降温速率变化而变化,其直流磁化率也未受很大影响.高温热电势弱的温度依赖关系表明为极化子气体的贡献.热电势在转折温度Tdrop之下的快速降低是由于二维反铁磁涨落的贡献.热电势在更低温度的拐点TS与载流子的局域化有关.降温速率变化时,Tdrop和TS都有明显的变化.Zn掺杂对Tdrop和TS没有明显影响,但导致了更强的载流子局域化.讨论了上述现象产生的物理图像 关键词： La2CuO4 直流磁化率 热电势     

簇合物(I2InN3)n (n=1-4)的结构和稳定性的理论研究

为寻求单一源前驱体,采用密度泛函理论DFT-B3LYP方法系统研究新的第IIIA主族叠氮簇合物的结构与性质关系。结果表明,簇合物(I2InN3) n (n=2-4)的优化构型均为由不同子体系的叠氮基α−N和In原子相连形成的环状结构,叠氮基以直线型存在。研究了几何参数随聚合度的变化趋势,并对计算获得的IR谱进行归属。能量和聚合焓均揭示簇合物的稳定性次序为3A>3B和4B>4C>4A>4D。簇合物(I2InN3)n (n=1-4)的热力学函数随温度升高和聚合度n增大而増加。热力学分析表明聚合反应在温度高达500 K均可自发进行。     

簇合物(I2InN3)n(n=1～4)的结构和稳定性的理论研究

为寻求单一源前驱体,采用密度泛函理论DFT-B3LYP方法系统研究新的第ⅢA主族叠氮簇合物的结构与性质关系.结果表明,簇合物(I2InN3)n(n=2～4)的优化构型均为由不同子体系的叠氮基α-N和In原子相连形成的环状结构,叠氮基以直线型存在.研究了几何参数随聚合度的变化趋势,并对计算获得的IR谱进行归属.能量和聚合焓均揭示簇合物的稳定性次序为3A＞3B和4B＞4C＞4A＞4D.簇合物(I2InN3)n(n=1～4)的热力学函数随温度升高和聚合度n增大而增加.热力学分析表明聚合反应在温度高达500 K均可自发进行.     

Dielectric characteristics of CaCu3Ti4O12/P(VDF-TrFE) nanocomposites

Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu₃Ti₄O₁₂ (CCTO) particles are used as filler and P(VDF?CTrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50?vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50?vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (??340?K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles.     

AC conductivity and dielectric behavior of polyaniline/sodium metavenadate (PANI/NaVO3) composites

The conducting polyaniline/sodium metavenadate (PANI/NaVO₃) composites were synthesized by single step in situ polymerization technique by placing finely grinded powder of NaVO₃ during the polymerization of aniline. The formation of mixed phases of the polymer together with the conducting emeraldine salt phase was confirmed by spectroscopic techniques like FTIR. SEM images indicated a systematic morphological variation of particles aggregated in the composite matrix as compared to the pristine PANI. AC conductivity and dielectric behavior of these composites were investigated in the frequency range 50 Hz to 5 MHz. It is found that AC conductivity obeyed the power law index and the variation of conductivity with wt% of NaVO₃ could be related to conductivity relaxation phenomenon. These composites have shown high dielectric constant, which is related to polarization. It is seen that both dielectric constant and dielectric loss decrease with increase in frequency. Variations in measured parameters of AC response with increasing frequency of these composites are found to follow systematic trends that are similar to those observed with temperature and doping.     

Dielectric permeability of the quasi-one-dimensional charge transfer salts: Qn(TCNQ)2 and NMeAd(TCNQ)2

The dielectric constant and conductivity of the high conductivity organic charge transfer comples salts Qn(TCNQ)₂ and NMeAd(TCNQ)₂ are measured at 9.1 GHz in the temperature range 4–320 K. The large increase with temperature of the dielectric constant is at variance with theoretical models describing the systems as metals or semiconductors at high temperatures. A model of localised states requires unreasonably large dipole moments in the excited state to fit with observations.     

The 38 K transition in TTF-TCNQ viewed as a percolation phenomenon

The d.c. conductivity, static dielectric constant and thermopower of TTF-TCNQ have been calculated for temperatures below 54 K within a self-consistent effective medium approximation. TTF-TCNQ is assumed to consist of small regions which are semiconducting and others which are highly conducting. The conducting regions have a large negative dielectric constant, a large d.c. conductivity and a negative thermopower; the semiconducting portions have a large positive dielectric constant, an activated d.c. conductivity and a large positive thermopower. The volume fraction of conductor increases from zero at T = 0 to unity at 54 K. The model is the first to reproduce the observed metal-insulator transition (e.g. the d.c. conductivity anomaly) near 38 K. The dielectric constant is calculated to rise initially with temperature and then become negative as the temperature increases above 38 K. The thermopower changes sign below 54 K and increases very rapidly at 38 K.     

铌酸锂钠在低温时的介电铁电和热电性

在300—20K的温度范围内观测了用丘克拉斯基法生长的Li_0.025Na_0.975NbO₃晶体的介电、铁电和热电特性。介电常数,极化强度和热电性的反常表示该晶体在低温时发生相变。此相变有特别大的热滞(约80K),降温时发生于180K附近,升温时发生于260K附近。测量了晶体的室温结构,指出了可能的低温相点群。观测了热电电荷的时间响应,报道了热电电荷随时间改变符号的特异现象,认为其起因是相变过程中两相共存。 关键词：     

A comparative study of magnetic and dielectric behaviors for La(1-x)Bi(x)Mn(1-y)Fe(y)O3 series (with x = 0.5, 0.7 and y = 0.3, 0.7)

We have carried out an extensive investigation into the effect of doping on both the A- and B-sites for the multiferroic La(0.5)Bi(0.5)Mn(0.5)Fe(0.5)O(3) in relation to its physical properties. The temperature dependent magnetization and dielectric response are determined for different percentages of Bi- and Fe-substitutions. For La(0.5)Bi(0.5)Mn(0.7)Fe(0.3)O(3), there is a prominent ferromagnetic transition T(C) around 110 K, whereas the other La(0.5)Bi(0.5)Mn(0.3)Fe(0.7)O(3) and La(0.3)Bi(0.7)Mn(0.3)Fe(0.7)O(3) phases fail to exhibit any clear transition. On the other hand, for the Fe-rich phases, the coercive field increases to 2450 Oe compared to 1720 Oe (for the Mn-rich phase). All the compositions exhibit coexistence of ferromagnetic and antiferromagnetic phases at low temperatures. The temperature dependent dielectric constant of the investigated samples varies from 32,000 to 500 at room temperature and the data has been analyzed using the universal dielectric response model.     

Temperature dependence of dielectric behaviour of illuminated HgI2

The real part of the dielectric constant was studied in the temperature range of 340 to 10 K, and at frequencies that range from 1 to 10⁴ Hz. The dipole contribution to the dielectric constant has been found at temperatures lower than 110 K while the space-charge contribution due to the increase of crystal defects is dominant at temperatures higher than 290K.     

Phase transition of [(C6H5)3PCH3]+(TCNQ)-2 and electrical transport properties

The electrical conductivity at 10GHz, the dielectric constant, and the thermoelectric power (TEP) of [(C₆H₅)₃PCH₃]⁺(TCNQ)^-₂, from 230 up to 400 K, have been measured. This organic quasi-one-dimensional solid undergoes a first order phase transition at 314 K. At the transition the conductivity increases by a factor of 2.2 and the activation energy drops to 0.26 from 0.31 eV. At 314 K TEP decreases abruptly from -75 to -60μVK^-1 and remains almost constant for T > 314 K. The dielectric permeability ?₀ is constant and equal to 5 in the low temperature phase, increases abruptly by 7% at the transition, and then depends strongly on temperature in the high temperature phase. Results of the high temperature phase are interpreted in terms of a strongly correlated salt.     

Pressure and temperature dependence of the static dielectric constant of KBr

The static dielectric constant and the temperature and pressure derivatives of the static dielectric constant of KBr have been measured at several temperatures between 4·3°K and room temperature. The sample was prepared in the form of a three-terminal parallel-plate capacitor and the dielectric constant was determined from measurements of the capacitance with a high precision bridge. The dielectric constant decreases with temperature as does the magnitude of the temperature dependence and the magnitude of the pressure dependence. The data were used to calculate the fixed-volume temperature derivative of the dielectric constant. This quantity, (? ln ε/?T)_v, exhibiting lattice-anharmonicity effects, decreases slightly from its room temperature value as the temperature is lowered, rises to a maximum value at about 33°K and then decreases rapidly at lower temperatures.