Sr位Nd掺杂对SrBi$lt;sub$gt;2$lt;/sub$gt;Nb$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;9$lt;/sub$gt;性能的影响及机理研究

采用传统固相法制备了（Sr_1-3x/2A_x/2Nd_x）Bi₂Nb₂O₉（x=0,0.05,0.1和0.2）陶瓷,并系统研究了Nd离子取代Sr离子对SrBi₂Nb₂O₉性能的影响及其作用机理.研究结果表明：Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉的介电常数和介电损耗随温度变化的行为具有明显的离子松弛极化特征.Nd³⁺对Sr²⁺的部分取代,导致Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉剩余极化强度P_r稍有下降,但其压电系数d₃₃却有所增加,根据铁电热力学理论,这是Nd³⁺对Sr²⁺取代导致材料介电常数增大所致.Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉的居里温度（T_C）没有随Nd含量的增加而变化,拉曼光谱技术分析表明这是其NbO₆八面体畸变程度没有发生变化所致.Nd³⁺取代Sr²⁺提高了材料的介电常数ε_r、压电系数d₃₃、机电耦合系数K_p,同时降低了机械品质因数Q_m,但是谐振频率温度系数C值没有改变. 关键词： 压电陶瓷 介电性能 压电性能 拉曼光谱     

Bi3+掺杂对Sr2MgSi2O7∶Eu2+荧光粉的结构及发光性能的影响

采用溶胶-凝胶法在还原气氛下制备了Sr₂MgSi₂O₇∶Eu²⁺,xBi³⁺(x=0,0.02,0.04,0.06,0.08,0.1)荧光粉,并用XRD、TG-DTA及激发与发射谱仪对样品的结构及发光性能进行了表征。结果发现:单掺杂Bi³⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为286 nm的宽带谱,这是由于激发态时Bi³⁺的³P₁→¹S₀电子能级跃迁而造成的;单掺杂Eu²⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为358 nm的宽带谱,这是典型的Eu²⁺的4f⁶5d¹→4f⁷跃迁而引起的。当Bi³⁺离子掺杂到Sr₂MgSi₂O₇∶Eu²⁺样品的摩尔分数为0.04时,样品的发射强度是未掺杂Bi³⁺离子样品的1.9倍。     

蓝色长余辉材料Sr2MgSi2O7：Eu2+,Dy3+及其基质的VUV-UV激发特性

Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺是一种有效的蓝色长余辉材料,采用高温固相法合成了Sr₂MgSi₂O₇,Sr₂MgSi₂O₇:Dy³⁺,Sr₂MgSi₂O₇:Eu²⁺及Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺,利用同步辐射研究了它们的VUV-UV激发特性.在真空紫外光激发下,在基质中发现了稍弱的位于385nm的发射带,在双掺杂的样品中,除了Eu²⁺的4f5d→4f发射带(465nm)外,还观察到了575nm处的发射峰;通过和Dy³⁺单掺杂样品的发射谱比较,发现它是来自于Dy³⁺的4f-4f(⁴F_9/2→6H_13/2)跃迁.在它们的激发谱上可以看出Dy³⁺与基质发射的有效激发均处于真空紫外区,在近紫外及可见区激发下未见到它们发光.另外在Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺中观察到Dy³⁺的发射也说明了Dy³⁺在该类长余辉材料中不仅作为陷阱用来延长余辉,而且也以发光中心形式存在于基质中.     

Sr3B2O6：Eu3+,Li+荧光粉的合成与发光性能

采用高温固相法合成Sr₃B₂O₆：Eu³⁺,Li⁺红色荧光粉,考察了激活剂Eu³⁺和电荷补偿剂Li⁺浓度对Sr₃B₂O₆：Eu³⁺,Li⁺荧光粉发光性能的影响。结果表明：适量掺杂Eu³⁺、Li⁺离子并不改变Sr₃B₂O₆的结构。当Eu³⁺掺杂量为4%、Li⁺的掺杂量为8%时,在900 ℃下灼烧2 h可以得到发光性能最佳的Sr_2.9B₂O₆：0.04Eu³⁺,0.08Li⁺红色荧光粉。以394 nm的近紫外光激发时,Sr₃B₂O₆：Eu³⁺,Li⁺荧光粉发射出红光,对应于Eu³⁺的4f-4f 跃迁,其中以614 nm附近的⁵D₀→⁷F₂跃迁发光最强,是一种有潜力用于白光LED的红色荧光粉。     

激发波长和Eu2+的掺杂量对Sr4Al14O25 ∶ Eu2+ , Dy3+发光性能的影响

采用溶胶-凝胶法在低温、还原气氛下制备了长余辉发光材料Sr₄Al₁₄O₂₅ ∶ Eu²⁺,Dy³⁺。用X射线粉末晶衍射对其进行了物相鉴定,表明在1 200 ℃已经得到纯相的Sr₄Al₁₄O₂₅ 产物。研究了铕和锶的比值、激发光波长对所制备的Sr₄Al₁₄O₂₅ ∶ Eu²⁺, Dy³⁺发光性能的影响并对其影响机理进行了探讨。样品的发光性能测试结果表明:采用溶胶-凝胶法制备长余辉发光材料Sr₄Al₁₄O₂₅ ∶ Eu²⁺, Dy³⁺,其灼烧温度比高温固相法灼烧温度低;激发光谱向长波方向延伸时,在488 nm处发射峰增强,在410 nm处发射峰减弱;在一定范围内发光强度随着Eu²⁺量的增加而增强,Eu²⁺的最佳掺杂量为0.007, Eu²⁺的掺杂量超过0.007时会发生浓度猝灭。     

铁电钨青铜型晶体SBN和KNSBN的Raman谱研究

测得了Sr_1-xBa_xNb₂O₆(SBN)和(K_1-yNa_y)_z(Sr_1-xBa_x)_l-zNb₂O₆(KNSBN)晶体的Raman谱,并用群论和晶格动力学观点进行了讨论.为其掺杂改性提供了科学依据. 关键词：     

Dy掺杂对Sr2Bi4Ti5O18铁电陶瓷性能的影响

用传统固相烧结法制备了Sr₂Bi_4-xDy_xTi₅ O₁₈(SBDT-x, x=0—0.20)陶瓷样品. x射线衍射分析表明, 微量的Dy掺杂没有影 响Sr₂Bi₄Ti₅O₁₈(SBTi) 原有的层状钙钛 矿结构. 通过研究样品的介电特性, 发现Dy掺杂减小了材料的损耗因子, 降低了样品铁电- 顺电相转变的居里温度. 铁电性能测量结果表明, 随Dy含量的增加, SBDT-x系列样品的剩余 极化先增大, 后减小. 当Dy掺杂量为0.01时, 剩余极化达到最大值, 约为20.1 μC·cm^-2. 掺杂引起剩余极化的变化, 与材料中缺陷浓度、内应力以及晶格畸变程度等因 素有关, 是多种作用机理相互竞争的结果. (Bi₂O₂)²⁺ 层通常被看作是绝缘层和空间电荷库, 对材料的铁电性能起关键作用. 掺杂离子进入(Bi2O₂)²⁺层会导致铁电性能变差. 关键词： 2Bi₄Ti₅O₁₈陶瓷')" href="#">Sr₂Bi₄Ti₅O₁₈陶瓷 Dy掺 杂 铁电性能 居里温度     

Sr2MgSi2O7∶Eu2+,Eu3+发光性能及颜色调控

采用静电纺丝法在不同气氛下制备了Sr₂MgSi₂O₇∶Eu²⁺,Eu³⁺纤维,研究其晶体结构和形貌;将纤维与聚二甲基硅氧烷(PDMS)复合后获得Sr₂MgSi₂O₇∶Eu²⁺,Eu³⁺-PDMS复合材料,研究其光致发光和应力发光性能。研究结果显示,氮气、空气下制备样品的XPS图谱同时出现Eu²⁺和Eu³⁺结合能特征峰;在360 nm和395 nm激发下复合材料的光致发光光谱中,不但有Eu²⁺位于469 nm处的蓝色宽带发射,还包含Eu³⁺位于615 nm的多个红色窄带发射。因为Eu³⁺在电荷补偿下还原成Eu²⁺并在刚性结构保护下不被氧化,证实了Eu³⁺在Sr₂MgSi₂O     

基质组成对Eu,Dy共掺杂铝酸锶发光性能的影响

研究了基质组成对xSrO·yAl₂O₃:Eu²⁺,Dy³⁺体系长余辉发光性能的影响,并对其影响机理进行了探讨.XRD分析结果和长余辉发光性能表明,改变Al₂O₃/SrO比率可以获得长余辉发光性能较好的三种基质相:SrAl₂O₄:Eu²⁺,Dy³⁺、Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺和SrAl₄O₇:Eu²⁺,Dy³⁺.激发与发射光谱性能分析和余辉衰减特性分析结果表明,随着基质中Sr/Al比例的减小,激发光谱向短波方向延伸,发射峰蓝移,初始余辉亮度越高,余辉持续时间越长.热释光谱分析表明,贫锶相晶格中的陷阱深度与密度较大,因而显示出较好的长余辉发光性能.     

双层钙钛矿氧化物Sr2CrBO6 (B = Os,Re,W)电子结构和光学性质的第一性原理研究

Sr₂CrBO₆(B=Os, Re, W)被证实是具有最高磁转变温度的双钙钛矿氧化物.论文采用基于密度泛函理论的第一性原理方法,计算了Sr₂CrBO₆的电子结构和光学性质,并通过计算结果分析了二者之间的内在关系.总体来看,B位元素的改变对材料的电子结构和光学性质都产生了较大的影响.由能带结构的计算,Sr₂CrOsO₆为半导体,Sr₂CrReO₆和Sr₂CrWO₆为半金属.晶体介电函数虚部ε₂(ω)曲线在所考察的能量范围内存在明显的介电特征峰,论文结合态密度和能带结构讨论了这些介电峰所对应的电子跃迁过程. Sr₂CrOsO₆和Sr₂CrReO₆在可见光区域均有较强的吸收,其中,Sr₂CrReO₆在394 nm处的峰值吸收...     

Li2Mo2O6多晶材料的结构与电性能的研究

本文用固相反应烧结制备出Li₂Mo₂O₆多晶材料。经X射线分析、红外光谱和电子顺磁共振谱(EPR)的研究,确定了它的结构是Li₂Mo₂O₄和MoO₂两个晶相组成的烧结体。钼离子以四价状态存在于MoO₂晶相结构中。采用交流阻抗谱分析了晶界与温度变化的相关性。测得了样品的ln(σ_总T)-1/T 曲线是由两段直线和一段曲线所组成;总电导率化能σ_27℃=1.36×10^-3(Ω·cm)^-1,σ_115℃=1.49×10^-3(Ω·cm)^-1,σ_300℃=9.71×10^-3(Ω·cm)^-1,σ_370℃=2.42×10^-3(Ω·cm)^-1;电导活化能E₁=0.043eV,E₂=0.235eV,E_平均=0.76eV。采用维格纳极化电池法测得电子电导率σ_e,σ_e27℃=2.240×10^-5(Ω·cm)^-1,σ_e300℃=4.476×10^-3(Ω·cm)^-1。实验证明,室温下材料为固体电解质,300℃附近为良好的离子与电子混合导体。 关键词：     

Absolute sense of pyroelectric p3 and piezoelectric d33 coefficients in 3La (IO3)3.HIO3.7H2O

The pyroelectric coefficient p₃ in 3La(IO₃)₃.HIO₃.7H₂O has an average value 2.0×10^-5 Cm^-2 in the temperature range 152 to 240 K. The resistivity decreases from 10¹² to 10¹⁰ ohm-cm between 258 and 338 K. At 298 K, the piezoelectric coefficient d₃₃  19×10^-12CN^-1. Positive polarity is generated on (001) by increasing temperature or tensile stress. A displacement toward (001) by La³⁺ or H₃O⁺ ions of 1×10^-4 Å per K or 10⁶Nm^-2, or rotation of the water molecule or iodate ion dipoles by about 5 arc minutes per K or 10⁶Nm^-2, produces the observed polarity.     

Ferroelectric and optical properties of Ba6Ti2Nb8O30 single crystals

The dielectric, optical and non-linear optical properties of Ba₆Ti₂Nb₈O₃₀ single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m². The linear electrooptic constants were measured as r₃₃^T=(1·17±0·02)×10^?10 and r₁₃^T=(0·42±0·01)×10^?10 m/V. The non-linear optical coefficients were d₃₃=(15·1±2·0)×10^?12 and d₃₁=(11·0±2·0)×10^?12 m/V, which are comparable to those of Ba₄Na₂Nb₁₀O₃₀. Temperature dependences of δ₃₃ and δ₃₁ (Miller's δ) were found to be proportional to that of P_s.     

Ionic transport in the lithium nitride bromides,Li6NBr3 and Li1 3N4Br

The ionic and electronic conductivities of the lithium nitride bromides Li₆NBr₃ and Li_{1 3}N₄Br have been studied in the temperature range from 50 to 220°C and 120 to 450°C, respectively. Both compounds are practically pure lithium ion conductors with negligible electronic contribution. Li₆NBr₃ has an ionic conductivity Ω of 2 × 10^-6Ω^-1cm^-1 at 100°C and an activation enthalpy for σT of 0.46 eV. Li_{1 3}N₄Br shows a phase transition at about 230°C. The activation enthalpy for σT is 0.73 eV below and 0.47 eV above this temperature. The conductivities at 150 and 300°C were found to be 3.5 × 10^-6 Ω^-1cm^-1 and 1.4 × 10^-3Ω^-1cm^-1, respectively. The crystal structure is hexagonal at room temperature with $\text{a = 7.415 (1)}\text{A}\text{?}$ and $\text{c = 3.865 (1)}\text{A}\text{?}$.     

Protonic conductivity of solid UO2HPO4·3H2O

The electrical and electrochemical properties of the solid ionic conductor UO₂HPO₄·3H₂O were investigated within the temperature range from room temperature up to 673 K. The conductivity of a nondehydrated sample within the temperature range from 303 K (6.5 × 10^-3 S/m) to 350 K (2.5 × 10^-2 S/m), with the activation energy of 23 kJ/mol, is a consequence of the presence of crystal water, and originates, mostly, from the fast movement of protons across the network of molecules of water in a tunneling mechanism pattern. When heated, the conductor loses crystal water, which leads to a final change in the nature of the conductor and in the conductivity mechanism. The conductivity of the dehydrated salt UO₂HPO₄ (2.5 × 10^-4 S/m at 488 K), with the activation energy 44.04 kJ/mol, is considerably lower than the one mentioned above and can be attributed, to a great extent, to the movement of protons, most likely by a tunneling mechanism, through the less favourable structure formed by phosphate groups of the dehydrated salt. On being heated above 623 K for a certain time, the acid phosphate transforms into pyrophosphate, the conductivity of which is lower than that mentioned above. By means of electrochemical methods, the electrode processes were studied. It has been shown that H⁺ and UO²⁺ ions are reduced at the cathode, while the phosphate groups oxidize at the anode and O₂ is evolved.     

利用超声脉冲回波重合法测定铌酸锂单晶弹性常数CijE和CijD

本文从基本的压电Christoffel方程出发导出三角晶系3m点群压电晶体弹性常数的表示式。并采用10MHz射频超声脉冲回波重合法测量了沿LiNbO₃不同对称方向传播的声速,结合e_ij和ε_ij⁵给出了LiNbO₃全部弹性常数C_ij^E和C_ij^D。它们是C₁₁^E=19.8 关键词：     

(111)取向(Pb,La)TiO3铁电薄膜中90°纳米带状畴与热释电性能的研究

采用射频磁控溅射技术在Pt/Ti/SiO₂/Si(100)衬底上生长了掺镧钛酸铅(PLT)铁电薄膜.用X射线衍射技术(XRD)研究了PLT薄膜结晶性能，结果表明PLT薄膜为 (111)择优取向钙钛矿相织构.使用原子力显微镜(AFM)和压电响应力显微镜(PFM) 分别观察了PLT薄膜的表面形貌和对应区域的电畴结构.PFM观察显示PLT薄膜中存在90°纳米带状畴，电畴的极化为首尾相接的低能量的排列方式，带状畴的宽度为20—60nm.研究了PLT10铁电薄膜的制备条件与性能之间的关系.发现在优化条件下制备的PLT10铁电薄膜的介电常数ε_r为365、介电损耗tgδ为0.02，热释电系数γ为2.18×10^-8C·(cm²·K)^-1，可以满足制备非制冷红外探测器的需要. 关键词： PLT薄膜 电畴 PFM 极化     

NH4IO3晶体的压电性能

用干涉法测量了NH₄IO₃晶体的全部压电系数。结果为: d₃₁=35.2, d₃₂=23.4, d₃₃=55.9, d₂₄=-2.4, d₁₅=-9.5×10^-8 CGSE/DYN。 关键词：     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

Specific features of the pyroelectric properties of actual RbTiOPO4 single crystals in the temperature range 4.2–300 K

The pyroelectric properties of samples cut from various growth sectors of RbTiOPO₄ single crystals grown from solution in a melt were measured in the temperature range from 4.2 to 300 K. The experimental values of the pyroelectric coefficient range from ?1.3 × 10^?5 to ?4.6 × 10^?5 C/m² K. For the samples cut from the (100) sector, pronounced anomalies were revealed at 85 and 275 K, which, in our opinion, can be due to the contribution of associates formed by the coordination tetrahedra PO₄(1) and PO₄(2) and interstitial rubidium Rb _i . At T > 280 K, superionic conductivity begins to manifest itself in all of the samples studied, which indicates the decomposition of the dipole complexes with increasing temperature. From the measured pyroelectric coefficient and birefringence along the polar direction, the spontaneous polarization of rubidium titanyl is calculated to be 0.5 C/m² at 250 K, which is comparable in magnitude to that of lithium tantalate.