纳米La3+-Eu3+共掺杂CeO2基固溶体的合成及微结构表征

采用水热法合成La3+、Eu3+共掺杂纳米Ce1-x(La0.5Eu0.5)x O2-δ固溶体。利用X射线衍射技术(XRD)表征样品的相结构,并对固溶体的晶胞参数进行拟合。通过拉曼光谱及紫外可见漫反射光谱表征其电子跃迁性能及掺杂效应。XRD结果表明,双离子掺杂固溶限不小于x=0.30,样品晶粒尺寸小于20 nm,晶胞参数随着掺杂量的升高而逐渐增大。Raman光谱F2g振动峰的逐渐宽化及向低波数方向移动。紫外漫反射光谱表明,随着掺杂量的增大,固溶体能隙先蓝移后红移。     

PDP绿色荧光粉BaAl12O19:Mn2+基质的单相合成研究

研究了Ba含量及掺杂Mg、Sr对基质BaAl12O19单相合成的影响.Ba含量的研究结果表明,Ba1 xAl12O19 x中Ba含量在1.1～1.2时,α-Al2O3和BaAl2O4相可以达到不被XRD检出的水平.掺杂Mg的实验结果表明,Mg的掺入可以使部分衍射峰消失,能够显著改善BaAl12O19的结晶状况,Ba1.2MgyAl12-yO19.1-y/2中Mg含量在0.8～1.1时可以形成很纯净的单相.掺Sr使部分衍射峰向高角度方向漂移,当Ba1.2-zSrzMg0.8Al11.2O18.8中Sr的掺入量为0.4时得到了更为纯净的单相,此时BaAl12O19:Mn2 的发光强度显著高于不掺杂样品.     

Sm2O3掺杂PbTiO3陶瓷的制备与电性能研究

采用溶胶-凝胶法制备了Sm2O3掺杂的PbTiO3陶瓷,并对其制备条件和电性能进行了研究.结果表明Sm2O3掺杂能够缩短凝胶形成时间,降低PbTiO3陶瓷烧结温度,改善烧结性能;Sm2O3掺杂PbTiO3陶瓷的电阻率均低于纯PbTiO3陶瓷,当掺杂量为0.003(n(Sm2O3)∶n(PbTiO3))时,电阻率最低,为5.8×108Ω*m;通过XPS分析,得到了Sm2O3掺杂PbTiO3陶瓷中各元素的结合能位置,表明Sm3+、Ti4+等都存在着不同程度的变价,导致了PbTiO3陶瓷导电性的提高.     

双钙钛矿化合物Sr2Mn1-xGaxMoO6（x=0,0.1,0.2,0.3）的晶体结构与磁性

用非磁性Ga3+部分替代Sr2MnMoO6中的Mn2+,获得Sr2Mn1-xGaxMoO6(x=0,0.1,0.2,0.3)多晶样品,通过X射线衍射(XRD)分析和磁性能测量研究Ga3+对晶体结构和磁性的影响。XRD谱Rietveld结构精修分析表明,Sr2Ga1-xMnxMoO6具有四方对称晶体结构(空间群I4/m)。随着Ga含量增加,B/B-原子占位有序度降低,平均键长减小,而平均键长增大,平均键角保持180o不变,平均键角逐渐扩张。5 K及300 K温度下,样品均为反铁磁体,但低掺杂样品在低温(5 K)下表现出微弱的铁磁性。上述结果表明,Ga3+对Mn2+的电子掺杂引起部分Mo离子价态由+6价转变为+5价。     

氧化钆对钛酸钡陶瓷结构和介电性能的影响

采用固相法制备得到了掺杂 1% (mol) Gd2 O3的钛酸钡陶瓷 ,并通过 X射线衍射分析和扫描电镜对其结构进行了表征。对其介电常数、介电损耗和室温电阻率进行了测定 ,结果表明 Gd2 O3掺杂 Ba Ti O3陶瓷的介电常数明显增加 ,介电损耗也有所升高 ,室温电阻率明显降低     

La_(0.5)Sm_(0.2)Sr_(0.3)MnO_3/Ag_x二相复合体的结构及磁电阻

用固相反应法制备La0.5Sm0.2Sr0.3MnO3/(Ag2O)x/2(x=0.00,0.04,0.08,0.25,0.30)样品,通过X射线衍射谱线(XRD),扫描电子显微镜(SEM)照片及SEM能谱(EDS),ρ-T曲线,研究样品的输运行为及磁电阻效应。结果表明:少量掺杂时Ag全部挥发。掺杂量较多时,挥发后多余的Ag主要以金属态包覆在母体颗粒的表面,使体系形成两相复合体。掺Ag为30%摩尔比时,样品的电阻率较低掺杂样品的电阻率降低一个数量级,在300K、0.5T磁场下,磁电阻明显增强,达到9.4%,这与颗粒母体界面结构的改善有关,也与材料电阻率的降低有关。     

Y~(3+)掺杂高介低损耗钛酸锶钡陶瓷的研究

为获得高介电常数低介电损耗的钛酸锶钡陶瓷,采用固相反应法制备了Y~(3+)掺杂BST_(60),BST_(65),BST_(70)陶瓷。用X射线衍射(XRD)、扫描电子显微镜(SEM)和阻抗分析仪,对陶瓷的微观结构和介电性能进行了测量。研究发现,Y~(3+)的掺入并未改变陶瓷母体结构,Y~(3+)在BST中形成了连续固溶体。最佳烧结温度处,随Ba/Sr比增大,晶粒尺寸增加;同一Ba/Sr比下,掺杂Y~(3+)能促进晶粒生长,由开始的平均1μm增大为3μm~4μm,尺寸连续分布,致密度提高。适量Y~(3+)掺杂有利于提高材料介电常数,降低介电损耗。当烧结温度为1450℃,Y~(3+)掺杂量为0.3%(摩尔分数)时,BST_(70)陶瓷相对密度为95.7%,介电常数最大为27891;此时BST_(65)介电常数为17811,损耗最小为0.00869,频率稳定性最好。     

Sm2O3对Ba0.5Sr0.5Co0.75Fe0.25O3-δ体系电子结构及氧空位影响的理论研究

采用第一性原理对掺杂Sm2O3的Ba0.5Sr0.5Co0.75Fe0.25O3-δ体系的电子结构和空位形成能进行了研究。研究结果表明,Co和Sm的态密度在费米能级附近有较大的态,而Fe则很小,这使得Co和Sm离子易于变价,而Fe离子的化合价则基本保持不变。空位形成能随空位数的增多而增大,Sm的掺杂有利于氧空位的形成,且CoVFe比CoVCo型氧空位形成能稍大,这些源于体系的电子结构和局域几何结构。     

Na和Al双掺杂P型Bi0.5Sb1.5Te3热电材料的制备及性能研究

采用真空熔炼及热压烧结技术制备了Na和Al双掺杂P型Bi0.5Sb1.5Te3热电材料。利用X射线衍射(XRD)、扫描电子显微镜(SEM)对样品的物相结构和表面形貌进行了表征。XRD分析结果表明,Na0.04Bi0.5Sb1.46-x Al x Te3块体材料的XRD图谱与块体材料Bi0.5Sb1.5Te3的图谱完全对应,所有块体材料的衍射峰均与衍射卡JCPDS 49-1713对应,这表明Na和Al元素已经完全固溶到Bi0.5Sb1.5Te3晶体结构中,形成了单相固溶体合金。SEM形貌表明材料组织致密且有层状结构特征。Na和Al双掺杂提高了Bi0.5Sb1.5Te3在室温附近的Seebeck系数。在Na掺杂量为0.04时,同时Al掺杂量由x=0.04增加至0.12,电导率逐渐降低,在实验掺杂浓度范围内,Na和Al双掺杂会使P型Bi0.5Sb1.5Te3材料的电导率受到较大的损失。在300~500 K时,通过Na和Al部分替代Sb,Na0.04Bi0.5Sb1.42Al0.04Te3和Na0.04Bi0.5Sb1.38Al0.08Te3样品的热导率均有不同程度地减小,在300K时双掺杂样品Na0.04Bi0.5Sb1.42Al0.04Te3的最大ZT值达到1.45。     

Nb掺杂(Bi0.5Na0.5)0.91Pr0.02Ba0.07TiO3无铅弛豫铁电陶瓷储能性能研究

通过固相烧结法掺杂微量Nb到(Bi_0.5Na_0.5)_0.91Pr_0.02Ba_0.07TiO₃无铅铁电陶瓷，对其相结构、微观形貌、储能行为及介电行为进行了研究。所有样品都形成了单一的钙钛矿相，晶粒细小，Nb掺杂有效地抑制了晶粒长大，在保持较大饱和极化强度基础上降低了剩余极化强度且提高了(Bi_0.5Na_0.5)_0.91Pr_0.02Ba_0.07TiO₃铁电陶瓷电场强度。掺杂量为0.05 mol时陶瓷在场强139 kV/cm下最大可释放储能密度达到1.85 J/cm³,储能效率达到65.75%,获得了较大的介电常数1250且保持稳定。     

Study on Dy2O3-Doped Medium Temperature Sintering (Ba,Sr)TiO3 Series Capacitor Ceramics

The influence of Dy₂O₃ doping on the properties of medium temperature sintering (Ba, Sr)TiO₃ series capacitor ceramics was studied by single factor various amount method, and the law of the influence on the medium temperature sintering (Ba, Sr)TiO₃ series capacitor ceramics was obtained. The dielectric materials used for multilayer ceramic capacitor was obtained, of which the dielectric constant was 1375, the dielectric loss was 0.0060, the density was 5.92 g·cm⁻³, the sintering temperature was less than 1150 °C, the capacitance temperature changing rate (ΔC/C) was less than ± 15%, the voltage withstand strength was more than 9.3 kV·mm⁻¹, and the crystal grain size was about 1 μm. The surface morphology of the sample doped with various amount Dy₂O₃ was analyzed by scanning electron microscope (SEM). The results showed that doping Dy₂O₃ could form defect solid solution, stop grain growth, fine crystal grain, widen curie peak, obtaining high dielectric constant and low dielectric loss, capacitance temperature property was suited for X7R character, in the (Ba,Sr)TiO₃ series ceramics. At the same time, the voltage withstand strength was enhanced greatly.     

Study on Red Long-Time Luminescent Material Y2O2S:Eu,M (M = Mg,Ca, Sr,Ba)

The red long-time luminescent material Y₂O₂S:Eu³⁺, M (M = Mg, Ca, Sr, Ba) was prepared by high temperature solid-state method. The XRD result of the sample showed that the crystal phase was Y₂O₂S, which belong to hexagonal system, and no new crystal phase were by doping different amount of Mg, Ca, Sr, Ba. The excitation spectrum was a broad band within 200 × 400 nm region, the characteristic peaks of emission spectrum were located at 583, 595, 597, 617, 627, 707 nm. There was no marked change in excitation spectra, emission spectra and maximum of their wavelengths of the luminescent materials by doping with different ions. The luminescent intensity of the phosphors were stronger when the concentration of doping ions was Mg/Y = 6%, Ca/Y = 4%, Sr/Y = 8%, Ba/Y = 2.5%, respectively. Its sequence of luminescent intensity from high to low is Sr > Ba > Mg > Ca.     

Dielectric Properties of Dy2O3 -Doped ( Ba, Sr) TiO3 Ceramics

The effects of Dy2O3 doping on the dielectric properties of (Ba, Sr)TiO3 series capacitor ceramics prepared using solid-state reaction method were studied. With the increasing of Dy2O3 additive , the dielectric constant (ε) of materials increases to a maximum when w(Dy2O3 ) is about 0.5% ,while the dielectric loss(tanδ) decreases. The BST ceramics with highε ( = 5245 ), low tanδ ( = 0. 0026 ) and high DC breakdown voltage ( = 5.5 mV ·m-1 ) were obtained. The influencing mechanism of Dy2O3 on the dielectric properties of (Ba, Sr)TiO3 ceramics was studied, thus providing the basis for preparation of capacitor ceramics.     

XPS Study on Barium Lanthanum Magnesium Niobate

Relaxor-type ferroelectric perovskites attract a lot of attentions due to their excellent dielectric and electrostrictive properties. (Ba,La)(Mg,Nb)O3(BLMN) ceramics were synthesized from oxides by sintering in airs using a conventional mixed oxide process. Thermogravimetry-differential analyzer (TG-DTA) analysis shows that the fired temperature of the Ba(Mg1/3, Nb2/3)O3 is above 1627.2 K. From the study of X-ray diffraction (XRD) patterns, it is founded that the amount of the perovskite phase increases with the increasing amount of La2O3. Furthermore, by the X-ray photoelectron spectroscopy (XPS) analysis, it is discovered that the amount of Nb4 is increased as La2O3 dopant increases from 0 to 0.04.     

钛酸锶钡陶瓷的制备及介电性能

采用固相法和溶胶凝胶法制备钛酸锶钡(BaxSr1 xTiO3,BST)粉末,用X射线分析仪(XRD)和扫描电镜(SEM)分析2种方法制备的BST粉末的物相组成和显微形貌。固相法和溶胶凝胶法所得粉末制备的压坯分别在1 400℃和1 300℃烧结2 h得到BST陶瓷,用密度分析仪、扫描电镜(SEM)和阻抗分析仪对BST陶瓷的密度、断口显微形貌和介电性能进行分析,研究不同Ba/Sr比例和2种不同粉末颗粒尺寸对BST陶瓷介电性能的影响。结果表明:室温下,BaxSr1 xTiO3(x=0.5,0.6)为立方相,BaxSr1 xTiO3(x=0.7,0.8)为四方相;固相法粉末制备的BaxSr1 xTiO3(x=0.5,0.6,0.7,0.8)陶瓷的密度、颗粒尺寸和介电常数峰值均随Ba含量的增加而增加,居里温度随Ba含量的增加呈线性增加,线性拟合得到Tc=221.6+354x,BST陶瓷的介电常数随频率的增加而降低;与固相法粉末制备的BST陶瓷相比,溶胶凝胶法粉末制备的BaxSr1 xTiO3(x=0.5,0.6)陶瓷密度较高,但同时出现介电峰弥散,介电常数和介电损耗较低。     

Influence of A-site doping barium on structure,magnetic and microwave absorption properties of LaFeO3 ceramics powders

In this paper, the effect of Ba²⁺ ions A-site doping LaFeO₃ on structure, magnetic properties and microwave absorption properties was investigated by the sol–gel method. According to the TEM and FullProf refinement results, the structure of LaFeO₃ changes from orthogonal (SG: Pnma) to cubic (SG: Pm-3m) when the Ba doping amount is x = 0.4. The SEM image shows that the particles size tends to decrease with the increase of Ba content. The production of weak ferromagnetism indicates that Ba doping has a significant effect on the magnetic properties of LaFeO₃. The Neel temperature (T_N) decreases significantly with the increase of Ba doping amount. An appropriate amount of Ba doping can effectively increase the dielectric and magnetic loss of LaFeO₃ ceramics powders. The increase permittivity (ε′ and ε″) may be attributed to the hopping of the electrons between the Fe³⁺ and Fe⁴⁺ ions with the Ba²⁺ ions doping. The minimum reflection loss (RL_min) of La_0.9Ba_0.1FeO₃ at 6.72 GHz reaches ?30.04 dB, its effective bandwidth (RL ≤ ?10 dB) is 2.1 GHz, and the matching thickness is only 3.2 mm. These results indicate that Ba doping can effectively control the microwave absorption properties of LaFeO₃, especially in the C-band.     

Effects of Sr²⁺ on structure and luminescent properties of BaAl₁₂O₁₉:Eu phosphors

Ba0.9-ySryAl12O19:Eu0.1 phosphors were prepared by sol-gel technique,the crystalline structures of samples characterized by XRD,and the luminescence properties were investigated.The influence of crystallographic positions on the luminescent properties of Sr2+-doped BaAl12O19:Eu was investigated in detail.The results indicated that the crystal lattice of BaAl12O19:Eu was not influenced by the Sr2+ and doping Sr2+ in BaAl12O19:Eu enhanced the luminescent properties of the phosphors at the proper concentration of Sr2+.With the increasing of concentration of Sr2+ doped in BaAl12O19:Eu,the relative luminescent intensity of Ba0.9-ySryAl12O19:Eu0.1 strengthened and blue-shifted.     

Effect of Gadolinium Substitution on Dielectric Properties of Bismuth Ferrite

Multiferroic Bi1-xGdxFeO3(x=0, 0.05, 0.1, 0.15, 0.2) ceramics were prepared by conventional solid state reaction method. X-ray diffraction was carried out to characterize the crystal structure and to detect any possible impurities existing in these ceramics. Frequency dependence of dielectric properties of Bi1-xGdxFeO3 samples at room temperature was measured in a frequency range from 100 Hz to 1 MHz using an HP4294A precision impedance analyzer. For all the samples studied, the dielectric constant and dielectric loss decreases with increasing frequency in the range between 100 Hz and 1 MHz, as can be expected from a typical orientational dielectric relaxation process. There is no indication of any dips over the whole frequency range studied, which is in direct contrast with that reported previously. It is found that both dielectric constant and dielectric loss are strongly dependent on the Gd3+ content. The effect of introducing Gd3+ is to increase the dielectric constant and to decrease the dielectric loss for slightly doped sample Bi0.95Gd0.05FeO3: the dielectric constant of the sample at 1 kHz reaches 600, six times bigger than that for pure BiFeO3. Complicated dielectric behaviors are observed at higher doping levels. Furthermore, the substitution of rare earth Gd for Bi helps to eliminate the impurity phase in BiFeO3 ceramics. There is strong evidence that both lattice constants a and c of the unit cell become smaller as the Gd3+ content is increased. The dielectric constant and loss and their frequency responses can be varied dramatically by substitution of Gd.     

Lattice Effects in La-Sm-Ca-Mn-O

The doping effects of Sm in La0.67Ca0.33MnO3 oxide were studied. The results show that with increasing the doping amount of Sm the phase transition temperature of metal-insulator for the materials decreases monotonically, the cor-responding peak resistance increases rapidly, the Curie temperature decreases monotonically, and the magneto-resistance ratio increases quickly. The effects of Sm doping can be explained in terms of lattice effects.     

A comparison of Ce~（3＋） luminescence in X_2Z（BO_3）_2（X=Ba,Sr;Z=Ca,Mg） with relevant composition and structure

The VUV-UV spectroscopic properties of Ce3+ in Ba2Mg(BO3)2,Ba2Ca(BO3)2 and Sr2Mg(BO3)2 were compared,and the relation between the energy of the 4f→5d transition of Ce3+ and the coordination environments of substituted alkaline earth ions was discussed.The chromaticity coordinates of Ce3+ activated X2Z(BO3)2(X=Ba,Sr;Z=Ca,Mg) phosphors were changeable from blue to whitish and further to green range by varying the doping concentration of Ce3+ or the types of substituted alkaline earth ions upon 172 nm excitation.