Luminescence properties of K1/2Bi1/2TiO3:Pr3+ and Na1/2Bi1/2TiO3:Pr3+

The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects.     

超巨磁电阻材料Pr2/3Sr1/3MnO3薄膜输运性质的研究

对1/f噪声缺口的超巨磁电阻Pr2/3Sr1/3MnO3薄膜样品从10K到室温的热电势值进行了测量,热电势为负值,低温下随温度线性变化,表现为金属扩散热电势,在150K开始急剧减小,过渡到与温度T成反比的变化关系,与小极化子模型相符.结合在电阻极大温度附近对电阻和1/f噪声行为的讨论,对于发生在电阻极大温度附近的相变过程,结果支持源于相分离的渝渗模型.     

La1-x／2Pr1-x／2SrxCuO4的电输运性质和超导电性

La1-x/2Pr1-x/2SrxCuOy(LPSCO)多晶样品采用传统的固相反应法制备.X射线衍射表明:LPSCO具有典型的空穴搀杂的T-214相的结构.磁化率测量显示:Sr搀杂在0.05≤x≤0.30范围内具有超导转变;Tc随x的增大呈抛物线形式变化,且在x=0.18时达到最大值28K.电阻的测量显示:随搀杂量的增大,系统呈现从绝缘到半导体,最后到金属的导电行为的变化;在欠掺杂区,正常态电阻温度关系符合ρ(T)=ρ0 αT-ClnT;而在过掺杂区,对数项消失.本文从替代所引起的晶体结构和载流子特性变化解释了Sr掺杂样品的电输运行为和超导特性.     

Pr1/3Sr2/3FeO3中电荷有序现象的超声研究

系统研究了Pr1/3Sr2/3FeO3单相多晶样品在低温下的电荷输运性质和超声特性.电阻测量表明,Pr1/3Sr2/3FeO3在162K发生了电荷有序相变.而超声声速从室温开始就出现了明显的软化,在电荷有序温度附近达到最小值,随后又急剧硬化,同时伴随着一个巨大的衰减峰.分析指出这是由于电-声子相互作用导致的结果,该电-声子耦合可能起源于Fe4 的Jahn-Teller效应.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Emission analysis of Pr and Tm: Ca2Gd2W3O14 phosphors

5 mol% of Pr³⁺ and Tm³⁺ ions activated calcium gadolinium tungstate (Ca₂Gd₂W₃O₁₄₎ phosphors were synthesized by traditional solid state reaction method. Crystalline phase structure was identified from the X-ray diffraction (XRD) profiles. From the scanning electron microscopy (SEM) images, we have observed the agglomeration of the particles, and average grain size is around 40-300 nm. Using the energy dispersive X-ray analysis (EDAX) and Fourier transform infrared (FTIR) spectra, identified the elements and functional groups present in the prepared phosphors. The emission spectrum of Pr³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown an intense red emission at 615 nm with the excitation wavelength λ_exci=450 nm and thus these red color emitting powder phosphors are used as one of the components in the preparation of WLEDs. The excitation spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ powder phosphor has shown a ligand to metal charge transfer (W-O) band (LMCT) within the WO₄²⁻ group. Emission spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ phosphors have shown blue emissions at 453 nm (¹D₂→³F₄).     

Anomalous behaviors in resistivity and magnetization of reduction-treated multi phase ceramics of Pr124/Pr123 and inhomogeneous Pr247

A superconductive sign found in electric resistivity behavior of mixed ceramic Pr124/Pr123 is searched and discussed, to advance preceding discussion about the superconductive region induced by intergrain charge transfer effect in ceramic Pr247 containing the related impurity phases. Observed reduction effects for largely impure ceramic of Pr247 with Pr124 and Pr123 and for simply dual-phase sample of Pr124/Pr123 inform us that the oxygen-reduction brings not only superconductive electron doping but also normal resistivity enhancement. Milder heat treatment condition is expected to assist possible attainment of zero-resistivity for Pr124/Pr123.     

纳米晶复合Pr2 Fe14 B/α-Fe永磁材料磁性的研究

采用熔体快淬的方法制备Pr2Fe14B/α-Fe纳米晶复合永磁材料.使用振动样品磁强计(VSM)测量样品的室温磁性能.实验合金成分为(PrxFe94.3-xB5.7)0.99Zr1(其中x=8.2,8.6,9.0,9.4,9.8,10.2,10.6,11.0,11.4(原子分数,%)).系统地研究了辊速及合金成分对快淬带磁性能的影响,当Pr原子分数由8.2%-11.4%变化时,矫顽力Hci升高,但剩余磁极化强度Jr却降低了,这是导致最大磁能积(BH)max下降的原因.当x=8.2(%)时,尽管样品的Hci较低,但高的Jr使(BH)max的值达到很高,在辊速为25m/s时得到最佳磁性能为:Jr=1.37T,Hci=501.19kA/m,(BH)max=227.93kJ/m3.同时发现垂直带面方向的Jr和(BH)max远高于平行带面方向.     

Magnetic and transport properties of the charge-ordered manganite Pr2/3Ca1/3MnO3

The transport properties, ac susceptibility χ, and EPR spectra have been studied for the insulator polycrystalline manganite Pr_2/3Ca_1/3MnO₃ undergoing the orbital (O) and charge (C) orderings below T _CO ～ 250 K that lead to antiferromagnetic (AF) ordering below T _N ≈ 155 K. Above T _C ～ 110 K, the χ′(T) dependence indicates that the sample contains a phase undergoing a second-order transition from the paramagnetic to ferromagnetic state. In the vicinity of T _C , the colossal magnetoresistance effect is observed. The EPR spectrum characteristics are sensitive to the development of the O/C and AF orderings, and they show peculiarities at T _CO and T _N . Between T _CO and T _N , the temperature dependence of the g factor exhibits a characteristic point that can be related to the appearance of the electric polarization revealed in manganites of this class.     

Hyperfine structure measurements in the4 I 9/2 ground state of141Pr

Using the atomic beam magnetic resonance method, the five hyperfine structure separations in the 4f ³ 6s ^{2 4}I_9/2 ground state of ₅₉ ¹⁴¹ Pr have been measured. The results are:F F′ E _FF′ ^* /h (MHz) 7 6 6477.913423(17) 6 5 5556.359848 (6) 5 4 4633.023306 (2) 4 3 3708.201146 (5) 3 2 2782.190601(15) From these quantities, the multipole interaction constantsA _k,k=1, 2, 3, 4 between the nucleus and the electron shell have been calculated.A ₄ especially then served to give the following limit for the intrinsic hexadecapole moment: ¦Q ₄₀¦<0.4eb ². Furthermore, theg _J -factors of the⁴ I multiplet have been measured at magnetic fields of 300 Oe. The results are:g _J(⁴ I _9/2)=0.7310371(15)g _J(⁴ I _11/2)=0.9651476(20)g _J(⁴ I _13/2)=1.1063197(40)g _J(⁴ I _15/2)=1.197963 (30) Small corrections due to perturbations by neighbouring fine structure levels are included.     

Quadrupole moment measurement of the highly deformed πg 9/2⊗νh 11/2 band in 130Pr

The quadrupole moment for the πg _9/2⊗νh _11/2 band in the ^130>Pr nucleus has been measured using the Doppler-shift attenuation method. A centroid shift analysis was carried out and a value of Q₀=6.1±0.4 eb, corresponding to an axial prolate deformation of β₂=0.35(3), has been determined. This is the first direct experimental confirmation of the deformation-driving character of the πg _9/2 orbital in an odd-odd nucleus in the A≃135 superdeformed region. Received: 23 April 1998     

纳米晶复合Pr2Fe14B/α-Fe快淬薄带的织构与磁性

采用快淬方法制备了纳米晶复合Pr₂Fe₁₄B/α-Fe永磁薄带，研究了不同淬火速率对薄带织构和磁性的影响.通过改善快淬工艺，使得薄带中Pr₂Fe₁₄B相的晶粒在薄带的自由面形成显著的织构，Pr₂Fe₁₄B相晶粒易轴沿垂直于带面方向取向.分析了快淬凝固过程中Pr₂Fe₁₄B相的晶粒取向过程和机理，以及晶粒的大小和薄带结构的均匀性对薄带磁性的影响.对自由面有显著取向的薄带，进行酸蚀和打磨减薄处理，去除贴辊面未取向的部分，剩余部分为具有Pr₂Fe₁₄B相晶粒取向的各向异性薄带，Pr₂Fe₁₄B相取向使薄带的剩磁得到增强，矫顽力也有所提高. 关键词： 快淬 2Fe₁₄B/α-Fe永磁薄带')" href="#">纳米晶复合Pr₂Fe₁₄B/α-Fe永磁薄带 织构 磁性能     

Crystal-field excitations in Pr2CuO4

Neutron spectroscopy has been employed to study the crystal-field excitations in Pr₂CuO₄. The energetic ordering of the crystal-field levels and the crystal-field parameters are determined from the observed transitions. Our results are consistent with the large magnetic anisotropy observed in single-crystal susceptibility data.     

A preliminary assessment of Lu2Y2Al2O9:Pr (LuYAM:Pr) as a potential scintillator

Lu₂Y₂Al₂O₉:Pr crystals have been grown by the micro-pulling-down method and their basic luminescence properties have been examined in order to estimate their utility for scintillator applications. The performed studies comprise the measurements of radioluminescence spectra as a function of temperature, photoluminescence emission and excitation spectra, and low temperature thermoluminescence glow curves. A comparison of the present results with those obtained recently for Y₄Al₂O₉:Pr indicates that in spite of a higher density Lu₂Y₂Al₂O₉:Pr is a much less promising material, which is mainly due to the absence of the fast Pr³⁺ d-f emission.     

Valence instability of Pr impurities in ZrIr2 and ZrOs2

This paper describes a search for valence instabilities of Pr impurities in ZrMe₂ with Me=Os, Ir and Ru. Pr impurities go into solution in the 2% concentration range in ZrIr₂ and ZrOs₂ but not in ZrRu₂. Susceptibility measurements indicate a nonmagnetic groundstate of Pr in both ZrIr₂ and ZrOs₂. The effective moment in ZrIr₂ is slightly below the trivalent value in ZrIr₂ while in ZrOs₂ the susceptibility is far below the trivalent value between helium and room temperatures. The resistivity increments of the alloys are very large and show very unusual temperature dependence, even for stable rare-earth (RE) impurities in ZrIr₂, where one observes strong deviations from the Matthiessen's rule at low temperatures. The depression of the superconducting transition temperature of ZrIr₂ and ZrOs₂ by Pr impurities is about 0.5 K/at%.