双钙钛矿Sr2Fe1-xNixMoO6(x=0.0～0.4)化合物的制备及其结构的研究

采用溶胶-凝胶法成功地制备了双钙钛矿结构的Sr2Fe1-xNixMoO6(x=0.0～0.4)化合物.X射线衍射实验表明,Ni的掺入没有改变化合物的晶体结构和空间群,但晶格常数随Ni含量的增加而减小,同时B位阳离子的占位有序度随Ni含量的增多而增大.研究还表明,B位阳离子的占位有序度与样品的烧结温度也有很大的关系,烧结温度升高,有序度增大.扫描电镜分析表明,所制备的样品颗粒度均匀,界面清晰,Ni的掺入使颗粒细化.     

双钙钛矿氧化物La_(2-x)Sr_xNiMnO_6(x=0,0.15)的电磁特性研究

采用固相反应法制备了双钙钛矿锰氧化物La_(2-x)Sr_xNiMnO_6(x=0, 0.15)样品。XRD测试结果表明,两个样品成相良好,属于钙钛矿晶体结构;通过磁化强度随温度变化曲线(M-T)可判定Sr掺杂导致样品铁磁性减弱,反铁磁性增强,等温磁化曲线(M-H)可进一步证实这一结论;两个样品的磁滞回线、2K下的磁滞回线的放大图和拉曼光谱测试结果可以共同说明Sr的掺杂使得系统反位无序度和反位缺陷增大、反位无序之间的反铁磁耦合增强、反铁磁性反相边界增加;同时χ~(-1)-T曲线在居里温度附近向上背离居里-外斯定律情况有减弱的趋势,用反位缺陷与反铁磁耦合强度之间相对强弱关系的变化可以解释这一现象;掺Sr之后,LSNMO系统的FCC和FCW曲线不重合是一级相变的典型特征,用重标定曲线和Arrott曲线可以进一步证实这一现象;同时两样品的电阻率随温度变化结果表明La_(1.85)Sr_(0.15)NiMnO_6的金属-绝缘体转变温度降低、在0和2T下测得的电阻率之间的差值增大。     

CeO_2掺杂对Pb_(0.92)Sr_(0.06)Ba_(0.02)(Sb_(2/3)Mn_(1/3))_(0.05)Zr_(0.48)Ti_(0.47)O_3基压电陶瓷相结构及性能的影响

采用传统固相烧结法制备Pb_(0.92)Sr_(0.06)Ba_(0.02)(Sb_(2/3)Mn_(1/3))_(0.05)Zr_(0.48)Ti_(0.47)O_3∶xCeO_2(简称PSBSM-PZT)压电陶瓷样品。研究不同CeO_2掺杂含量对PSBSM-PZT基陶瓷样品的物相结构、微观形貌、压电及介电性能的影响。结果表明:当CeO_2掺杂量x≤0.5%(质量分数,下同)时,陶瓷样品均为纯的钙钛矿结构。随着CeO_2掺杂含量的增加,陶瓷样品中四方相结构逐渐向三方相结构转变。随着CeO_2掺杂含量的进一步增加,陶瓷中出现焦绿石相,虽然陶瓷中已经出现焦绿石相,但是样品仍没有完全转变为三方相陶瓷;CeO_2掺杂具有细化晶粒的作用,当x=0.25%时样品晶粒晶界清晰,晶粒之间的结合相对致密,晶界处气孔率低,陶瓷断裂方式以沿晶断裂为主;当x=0.25%时,陶瓷样品获得最佳的压电与介电性能:d_(33)=346pC/N,k_p=0.60,Q_m=1396,ε_r=1309,tanδ=0.474%。     

ZnAl_2O_4和La_2O_3对Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷介电性能的影响

通过传统的固相反应合成掺杂ZnAl_2O_4和La~(3+)(来自La_2O_3)的Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷粉体,干压成型后在空气气氛下常压烧结制备ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品。分别研究了La~(3+)和ZnAl_2O_4的掺杂量对复合陶瓷样品的微观形貌、相组成和介电性能的影响。结果表明:ZnAl_2O_4具有细化晶粒的作用;Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品的致密度随La~(3+)和ZnAl_2O_4含量的增加而增加;介电常数和谐振频率温度系数随ZnAl_2O_4含量的增加而减小,随La_2O_3添加量变化不大;品质因数值随ZnAl_2O_4含量的增加先增加后减小。制备出的ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷致密度达到94%以上,介电常数在40~50之间,谐振频率温度系数小于40×10~(-6)℃~(-1),品质因数大于38 000GHz,可以用于通信技术领域。     

溶胶-凝胶法制备Sr掺杂La_(9.33-2x/3)Sr_x(SiO_4)_6O_2及其导电性研究

采用溶胶-凝胶法于900℃成功合成了Sr掺杂的La9.33-2x/3Srx(SiO4)6O2前驱粉体,然后于1450℃烧结成陶瓷样品。利用X射线粉末衍射和环境扫描电镜对材料的物相和形貌进行了分析和表征,结果表明合成产物为磷灰石相,烧结后样品晶体颗粒比较均匀,有较好的致密度。采用交流阻抗谱研究了材料的导电性,发现Ln位阳离子空位比Ln位阳离子掺杂对材料电导率的影响更大,合适的Ln位阳离子空位更有利于提高材料的电导率。     

Ca掺杂的GdBaCo2O5+δ的制备和物性研究

采用固相反应法制备了Gd1-xCaxBaCo2O5+δ(x=0、0.1、0.2)层状钙钛矿钴氧化物,通过XRD、SEM、TG和四线法研究了材料的制备和物理性能。结果表明,Ca掺杂的样品主相具有母相GdBaCo2O5+δ的晶体结构,还存在杂相BaCoO2.6;晶胞参数和体积随Ca掺杂量的增加而减小。从室温到1000K,所有样品都经历了金属绝缘体转变和结构相变,Ca掺杂样品的电导率得到大大提高,约为母相的2倍。     

化合物Sr1.98Nd0.02FeMoO6和Sr1.96Nd0.04FeMoO6的制备及磁学表征

采用溶胶-凝胶法制备了双钙钛矿氧化物Sr1.98Nd0.02FeMoO6和Sr1.96Nd0.04FeMoO6样品。X射线粉末衍射结果表明样品均为纯相,室温下空间群为I4/m,样品有序度随掺杂量的增加而降低。采用多功能振动样品磁强计表征了样品的磁滞曲线和磁热曲线,结果表明样品均具有铁磁性质。H/M-M2曲线表明两个样品均为二级磁相变。Nd掺杂导致样品的居里温度与磁矩降低。不同外磁场下的M-T曲线测量结果表明随着外部磁场的增加样品最大磁矩冻结,阻塞温度降低。     

双钙钛矿氧化物Pr(2-x)Tbx CoMnO6(x=0.00,0.05,0.10)的磁性研究

利用传统高温固相反应法制备了钙钛矿钴氧化物Pr_(2-x)Tb_xCoMnO_6(x=0.00,0.05,0.10)系列多晶样品,通过样品的XRD谱线、磁化强度随温度、外加磁场的变化曲线(M-T、M-H)等对样品的晶体结构和磁性进行了研究.结果表明:系列样品Pr_(2-x)Tb_xCoMnO_6(x=0.00,0.05,0.10)呈现良好的单相性,空间点群为P2_1/n;由于Co~(2+)与Mn~(4+)之间的铁磁超交换相互作用和少量无序的Co~(3+)与Mn~(3+)之间的铁磁超交换相互作用,3个样品均出现两个铁磁转变点(T_(C1)和T_(C2)),观察到系列样品存在类Griffiths相,温度TT_G则为纯顺磁态;在T_(C2)-T_G之间属于顺磁-铁磁共存状态;在低温区(TT_N时),铁磁态与反铁磁态相互竞争,出现了自旋团簇玻璃行为;随着Tb的掺杂,T_(C1)、T_(C2)、T_N和T_G均下降。在测量温区内,随着温度的降低,3个样品均先后经历了纯顺磁态、顺磁-铁磁共存态、铁磁-反铁磁相互竞争的过程。     

La0.5Ca0.5MnO3中Ca位上Ba掺杂效应研究

用固态反应法制备了具有单相结构的La_0.5Ca_0.5-xBa_xMnO₃系列样品,其结构随Ba含量增加由立方晶系转变为典型的正交晶系．零场下输运性质实验表明,在较低掺杂量时,系统在整个温区显示半导体型导电特征,而当掺杂量超过0.14时,系统发生由半导体到金属的转变,且转变的温度随掺杂量增加而移向高温瑞．基于对实验结果的分析,就Ca位上Ba掺杂所起的作用进行了初步探讨．     

Sr_(2-x)Ga_xFeMoO_6的磁学性能研究

采用固相反应法成功制备了双钙钛矿化合物Sr_(2-x)Ga_xFeMoO_6(x=0.00,0.03,0.05)。样品的X射线衍射图谱表明所有样品均为四方相结构,空间群为I4/m。通过样品的场冷曲线求得样品的居里温度分别为370、355、338 K。样品的低温磁化强度测量结果表明只需要很小的磁场就能使样品达到饱和状态。随着掺杂量的增加,样品的磁转变区间被扩宽。x=0.00样品的磁熵变最大值出现在居里温度附近,2.5T磁场下,最大磁熵变值为0.59 J/kg·K,相对制冷功率为68.88 J/kg。     

VLE data for CO2-CF2Cl2, N2-CO2, N2-CF2Cl2 and N2-CO2-CF2Cl

Knowledge about vapour-liquid (VLE) is required as a basis of reliable calculations for separation processes. Correlations available for the prediction of T, p, x, y data are less accurate for mixtures at high pressures and mixtures containing supercritical components. The results of VLE experiments are reported and compared with data calculated with equations of state.     

Thermal diffusion in binary mixtures H2-CCl2F2 and H2-CHClF2

Thermal diffusion coefficients were measured in two gaseous mixtures, in which one component was close to the critical temperature, in the pressure range (19.6–127.4)·10⁴ N/m² and at a freon concentration of 0.25–0.8.     

Preparation of ZrO2-CeO2 and HfO2-CeO2 nanopowders

We prepared weakly agglomerated powders of ZrO₂-CeO₂ and HfO₂-CeO₂ solid solutions 5–8 nm in particle size, consisting of monoclinic and tetragonal phases. After heat treatment at 1200°C, the crystallite size was 30 and 14 nm, respectively. We also examined the effect of precipitate freeze drying on the crystallization of hafnia-based solid solutions containing up to 20 mol % CeO₂.     

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

First-principles cluster calculations are reported of the local electronic structure of the three compounds: La₂CuO₄, Sr₂CuO₂Cl₂, and Sr₂CuO₂F₂. The copper ${\text{3d}}_{x^2 - y^2 } $ and the planar oxygen 2p _σ atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the ${\text{3}}d_{3z^2 - r^2 } $ atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.     

Radial GRIN glasses in Li2O-Na2O-Al2O3-TiO2-SiO2 systems

A series of GRIN glass rods have been developed in Li2O-Na2O-Al2O3-TiO2-SiO2 systems. Negative radial refractive index profiles were generated by exchanging Na+ for Li+ ions in these glass rods. It has been observed that TiO2 plays a vital role in increase in the profile depth and maximum change in the refractive index because of its ambivalent nature. Change in the refractive index can be further increased by increasing the concentration of exchanging cation in the base glass.     

Elastic and Electronic Properties of Superconducting CaPd 2 As 2 and SrPd 2 As 2 vs. Non-superconducting BaPd 2 As 2

The first-principles calculations were performed to predict the elastic and electronic properties of the superconducting ThCr₂Si₂-type phases CaPd₂As₂ and SrPd₂As₂ in comparison with the non-superconducting CeMg₂Si₂-type phase BaPd₂As₂. Besides, the same properties were compared for CeMg₂Si₂- and ThCr₂Si₂-type polymorphs of BaPd₂As₂. We found that all these phases are mechanically stable and belong to soft materials with low hardness. The near-Fermi region is formed by the valence states of the blocks [Pd₂As₂] with decisive contributions of Pd 4d states. The values of N(E _F) increase in the sequence: CaPd₂As₂ < SrPd₂As₂ < BaPd₂As₂, i.e. in the reverse sequence relative to the transition temperatures T _C. Thus, the change in T _C cannot be explained by the electronic factor, i.e. by the simple correlation T _C～N(E _F). Most likely the decrease in T _C in the sequence CaPd₂As₂ → SrPd₂As₂ and the absence of a superconducting transition in BaPd₂As₂ are related to the structural factors and the peculiarities of the electron–phonon coupling mechanism.     

Si_2N_2O-Al_2O_3-La_2O_3和Si_2N_2O-Al_2O_3-CaO系统的亚固相关系

本文给出了 Si_2N_2O-Al_2O_3-La_2O_3和 Si_2N_2O-Al_2O_3-CaO 系统的亚固相图。实验结果表明:在 Si_2N_2O-Al_2O_3-CaO 系统中有一个未知结构的新化合物 CaO·Si_2N_2O,在3CaO·Si_2N_2O 和3CaO·Al_2O_3两化合物之间形成连续立方固溶体。而 Si_2N_2O-Al_2O_3-La_2O_3系统中则没有发现新化合物。在两个系统的富 Si_2N_2O区,过量的 Si_2N_2O 与 La_2O_3和 CaO 分别反应形成 Si_3N_4与 La_(10)[SiO_4]_(?)N_2(H-相)(和 CaSiO_3。所研究的这两个三元系统中,分别形成了如下几个四元相容性区。在 Si_2N_2O-Al_2O_3-La_2O_3系统内有:H-Si_3N_4-La_2O_3·Si_2N_2O-La_2O_3·Al_2O_3;H-Si_3N_4-La_2O_3·Al_2O_3-La_2O_3·11 Al_2O_3;H-Si_3N_4-La_2O_3·11 Al_2O_3-Al_2O_3;H-Si_3N_4-Al_2O_3-O′s.s;H-Si_3N_4-O′s.s-Si_2N_2O在 Si_2N_2O-Al_2O_3-CaO 系统内有:Si_3N_4-CaSiO_3-CaO·Si_2N_2O-3CaO·Al_2O_3;Si_3N_3-CaSiO_3-3CaO·Al_2O_3-2CaO·Al_2O_3·SiO_(?);Si_(?)N_(?)-CaSiO_3-2CaO·Al_2O_3·SiO_2-Al_2O_3;Si_3N_4-CaSiO_3-Al_2O_(?)-O′s.s;Si_3N_4-CaSiO_3-O′s.s-Si_(?)N_(?)O