Jahn-Teller distortion and magnetoresistance in electron doped Sr1-xCexMnO3 (x = 0.1, 0.2, 0.3 and 0.4)

Neutron and electron diffraction, electrical transport and magnetic measurements have been carried out on a newly synthesized electron doped Sr_1-xCe _x MnO₃ (x = 0.1, 0.2, 0.3 and 0.4) system. For x=0.1, while cooling, it undergoes a first-order metal-insulator transition at 315 K which is associated with a structural transition from cubic (Pm3m) to tetragonal (I4/mcm) due to Jahn-Teller ordering () which stabilizes a chain like (C-type) antiferromagnetic ground state with . The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the d _x2-y2 symmetry. Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance appears for . Magnetic measurements show that the dilution of antiferromagnetic interaction results into a spin glass like behaviour at low temperature for the samples with x=0.3 and 0.4. This behaviour is in contrast with the CMR properties of calcium based electron doped systems and hole doped manganites. The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size may be responsible for the absence of double exchange ferromagnetism and CMR effect. Received 10 September 1999     

Synthesis and electrochemistry of LiNi0.6Fe0.3−xMg0.1+xO2 (x=0, 0.5 and 1.0) materials for lithium-ion batteries

Lithium nickel oxide cathodes doped with Fe and Mg was synthesized by the solid state reaction method at 800 °C. Structural investigation of these materials was performed using XRD and EDAX. The electrochemical behavior was studied using galvanostatic charge/discharge in order to investigate the performance of LiNi_0.6Fe_0.3Mg_0.1O₂, LiNi_0.6Fe_0.25Mg_0.15O₂ and LiNi_0.6Fe_0.2Mg_0.2O₂ materials. It is shown that LiNi_0.6Fe_0.3Mg_0.1O₂ produced about 96 m Ah/g of discharge capacity. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Nonlinear dielectric properties of amorphous Bi1.8Pb0.3Sr2Ca2Cu3−x KxOz (x = 0.2–0.3)

The dielectric constant of amorphous Bi_1.8Pb_0.3Sr₂Ca₂Cu_3?x K_xO_x (x = 0.2–0.3) is measured as a function of the static electric field strength. It is found that, as the field strength increases, the dielectric constant decreases following a quadratic law. This behavior of the dielectric constant in a static electric field indicates nonlinear dielectric properties, which can be described within the thermodynamic theory of ferroelectricity.     

Raman spectra of CuGaS2-x Se x (x=0, 0.5, 1.0)

Summary Raman spectra on the CuGaS_2-x Se _x system (x=0, 0.5, 1.0) are described for the first time. The observed structures are assigned on the basis of the analogies with binary solid solutions. The broadening of theA ₁ sulphur mode seems to indicate the effect of substitutional disorder. Paper presented at the ?V. International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Magnetic order in hybrid frustrated magnets Gd(2-x)Tb(x)Ti2O7 (x = 0.2 and 0.5)

We report on the specific heat, magnetization and ac susceptibility measurements of single crystals of hybrid frustrated magnets Gd(1.8)Tb(0.2)Ti(2)O(7) and Gd(1.5)Tb(0.5)Ti(2)O(7). The analysis of experimental data revealed that, although partial replacing of the Gd(3+) ions by the Tb(3+) ions in the Gd(2)Ti(2)O(7) host lattice slightly enhances antiferromagnetic coupling, as inferred from the evolution of the paramagnetic Curie-Weiss temperature, the ordering temperature gradually decreases. Paramagnetic correlations introduced by the Tb(3+) ions cause this perturbation, altering the effective further neighbor interactions and destabilizing the ground state in Gd(2)Ti(2)O(7). In addition, the low-energy states of Gd(2-x)Tb(x)Ti(2)O(7) are suggested to possess a nature different from those in parent members Tb(2)Ti(2)O(7) and Gd(2)Ti(2)O(7). Finally, the frequency-dependent magnetic susceptibility behavior in Gd(1.5)Tb(0.5)Ti(2)O(7) is consistent with the formation of a spin-glass-like state indicating a pronounced slowing down of the dynamical response of the studied hybrid magnets.     

Giant low-field magnetocaloric effect in EuTi_(1-x)Nb_xO_3(x = 0.05, 0.1, 0.15, and 0.2) compounds

The magnetic properties and magnetocaloric effect(MCE)of EuTi(1-x)NbxO3(x=0.05,0.1,0.15,and 0.2)compounds are investigated.Owing to electronic doping,parts of Ti ions are replaced by Nb ions,the lattice constant increases and a small number of Ti⁴⁺(3d^0)ions change into Ti³⁺(3d^1).It is the ferromagnetism state that is dominant in the derivative balance.The values of the maximum magnetic entropy change(-?SM^max)are 10.3 J/kg·K,9.6 J/kg·K,13.1 J/kg·K,and 11.9 J/kg·K for EuTi(1-x)NbxO3(x=0.05,0.1,0.15,and 0.2)compounds and the values of refrigeration capacity are 36,33,86,and 80 J/kg as magnetic field changes in a range of 0 T–1 T.The EuTi(1-x)NbxO3(x=0.05,0.1,0.15,and 0.2)compounds with giant reversible MCE are considered as a good candidate for magnetic refrigerant working at lowtemperature and low-field.     

Temperature dependence of infrared conductivity of manganites (x = 0, 0.05 and 0.2)

The temperature dependence of the reflectivity spectra of three manganites ceramics with compositions Pr_0.7Ca_0.3MnO₃, Pr_0.7Ca_0.25Sr_0.05MnO₃ and Pr_0.7Ca_0.1Sr_0.2MnO₃ has been investigated by infrared reflectivity spectroscopy in the wave number range 0.005-1.1 eV. The compound Pr_0.7Ca_0.25Sr_0.05MnO₃ which shows the largest conductivity jump at the ferromagnetic-paramagnetic phase transition has been studied in details. The optical conductivity of this compound is deduced from the best fit to reflectivity spectra of a “double-damping Drude” model, itself derived from the factorized form of the dielectric function. Excellent agreement with Kramers-Kronig transformation is reported. The model allows in particular to discriminate the contributions to the optical conductivity of trapped charges (polarons) and mobile charge carriers. Received 20 July 1999 and Received in final form 15 October 1999     

Magnetocaloric effect in polycrystalline (La0.5Gd0.2)Sr0.3MnO3

In this paper, we present a study of magnetocaloric effect in the colossal magnetoresistance material (La_0.5Gd_0.2)Sr_0.3MnO₃. From the measurements of isothermal magnetization at different temperatures, we have discovered a large magnetic entropy change with a broad peak around Curie temperature (270.5 K) in (La_0.5Gd_0.2)Sr_0.3MnO₃ polycrystalline sample. Moreover, the maximum of magnetic entropy change exhibits a nearly linear dependence with applied high magnetic field. These results suggest that this material is a suitable candidate as working substance in magnetic refrigeration near room temperature.     

Quasi two-dimensional magnetic order of Tb3+ spins in Pb2Sr2Tb1−x Ca x Cu3O8 (x = 0 and 0.5)

Neutron diffraction experiments were performed to study the magnetic ordering of the Tb⁺³ sublattice in the high-T _c superconductor Pb₂Sr₂Tb_1?x Ca _x Cu₃O₈ (x = 0.5) and the undoped parent compound (x = 0). For the parent compound, a quasi two dimensional (2D) phase with a finite antiferromagnetic correlation along the c-direction and a three dimensional phase with ferromagnetic correlation along the c-direction were found. The coexistence of the two phases is likely to be related to structural imperfections such as stacking faults, strains, oxygen disorder or cation vacancies. The superconductor with a superconducting transition temperature of T _c = 71K exhibits a quasi 2D magnetic ordering of the Tb sublattice with a finite ferromagnetic correlation along the c-direction. The correlation lengths along the c-direction for the quasi 2D phases are 32 and 26Å for x = 0 and 0.5, respectively. The magnetic saturation moments are with 9.1 and 8.8 μ _B in excellent agreement with our mean-field crystal-field calculations. 2D short range correlation could be observed up to about 8T _N and is described by a Lorentzian distribution of magnetic intensity perpendicular to the 2D rod in reciprocal space.     

Nd_(0.9)Ca_(0.1)Ba_2Cu_3O_(6+x)(x=0～1)超导体系的Raman光谱研究

Ｎｄ０．９Ｃａ０．１Ｂａ２Ｃｕ３Ｏ６＋ｘ（ｘ＝０～１）超导体系的Ｒａｍａｎ光谱研究赵芸１罗培勋２左健２许存义２李晓光２（１安徽机电学院芜湖２４１０００）（２中国科学技术大学结构分析开放研究实验室合肥２３００２６）ＳｔｕｄｙｏｎｔｈｅＲａｍａｎＳｐｅ...     

La诱导(Pb(1-3x/2)Lax)(Zr0.5Sn0.3Ti0.2)O3反铁电介电弛豫研究

采用标准电子陶瓷工艺制备了(Pb_(1-3x/2)La_x)(Zr_0.5Sn_0.3Ti_0.2)O₃(PLZST,0.00≤x≤0.18)反铁电陶瓷,利用X射线衍射、不同频率下弱场介电温谱、强场下的极化强度-电场(P-E)测试研究了材料相结构和电学性能.实验结果发现,随La含量x增大,室温下材料由铁电三方相(关键词： 反铁电陶瓷 介电频率色散 相变弥散 介电弛豫     

Erbium germanosilicide Ohmic contacts on Si_(1-x)Ge_x(x=0-0.3) substrates

We have studied erbium germanosilicide (ErSiGe) Ohmic contacts on n-type Si_(1-x)Ge_x substrates with differing Ge concentrations (0≤x≤0.3).Thin layers of Ti (20 nm)/Er (20 nm) were deposited on Si_(1-x)Ge_x substrates and then post-annealed at 600°C for 60 s to form a stable ErSiGe film.The structures of the ErSiGe films and ErSiGe/Si_(1-x)Ge_x interfaces were characterized by Transmission Electron Microscopy measurements (TEM).The TEM images showed that the thicknesses of ErSiGe films and the Si_(1-x)Ge_x...     

压力对La_(0.3)Bi_(0.2)Ca_(0.5)MnO_3中晶格畸变的影响

利用同步辐射X射线衍射技术 ,对La0 .3Bi0 .2 Ca0 .5MnO3 中存在的Jahn Teller畸变进行了原位的高压研究。实验表明 ,外加压力能有效地影响到晶格中Mn—O键长和Mn—O—Mn键角的变化。当压力为 1.8GPa时 ,在晶格中存在的两种不同畸变模式之间的相互作用下 ,导致了位于a b基面上的Q2 畸变模式的消失     

Critical Current Density,Vortex Pinning,and Phase Diagram in the NaCl-Type Superconductors InTe1-xSex(x = 0, 0.1, 0.2)

Research of vortex properties in type-Ⅱ superconductors is of great importance for potential applications and fundamental physics. Here, we present a comprehensive study of the critical current density Jc, vortex pinning,and phase diagram of Na Cl-type In Te_1-x Se_x(x = 0, 0.1, 0.2) superconductors synthesized by high-pressure technique. Our studies reveal that the values of Jc calculated by the Bean model exceed 10⁴A/cm² in the In Te_1-x Se     

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.     

Enhanced susceptibility in LNiO3 perovskites ( L = La,Pr,Nd,Nd0.5Sm0. 5)

The temperature dependence of the resistivity rho(T) and of the dc magnetic susceptibility chi(T) were measured on high-quality LNiO3 (L = La,Pr,Nd,Nd0.5Sm0.5) samples synthesized under high oxygen pressure. Subtraction of the rare-earth contribution to chi(T) allows the presentation of the evolution of the susceptibility of the NiO3 array from Pauli to Curie-Weiss paramagnetism with decreasing bandwidth. A metal-insulator transition occurring at a temperature T(t) = T(N) is first order for L = Pr and Nd; it becomes second order and produces no anomaly in chi(-1)(T) at a T(t)>T(N) for L = Nd0.5Sm0.5. In the antiferromagnetic domain T相似文献   

Characterisation of sol-gel prepared (HfO2)x(SiO2)1-x (x=0.1, 0.2 and 0.4) by 1H, 13C, 17 O and 29Si MAS NMR, FTIR and TGA

The HfO2-SiO2 system is attracting interest as a possible new dielectric material in semiconductor devices. Knowledge of the location of hafnium within the silica network and the effect hafnium has on the structure will be central to the successful use of this material system in this application. Here, sol-gel techniques have been used to manufacture (HfO2)x(SiO2)1-x samples (x=0.1, 0.2 and 0.4, each heat treated at 250, 500 and 750 degrees C) and these have been characterised by magic angle spinning (MAS) NMR (1H, 13C, 17 O, 29Si), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. 29Si MAS NMR showed that increasing the hafnia content decreases the connectivity of the silicate network, i.e. increases the range of differently connected SiO4 (Qn) units with more having increased numbers of non-bridging oxygens (i.e. lower n). FTIR and 17 O MAS NMR showed unequivocally that the x=0.4 sample phase-separated at higher temperatures, while in the x=0.1 sample the hafnium was homogeneously mixed into the SiO2 phase without any phase separation.     

Polarization properties of Li2−x Na x Ge4O9 (0.2 ≤ x ≤ 0.3) crystals

The polarization switching in sinusoidal fields and the pyroelectric properties of Li_2?x Na _x Ge₄O₉ (0.2 ≤ x ≤ 0.3) crystals are measured in the temperature range T _c ?T ≤ 40 K. The behavior of the P?E hysteresis loops with variations in temperature is investigated for crystals with phase transition temperatures T _c < 300 K and T _c > 300 K. It is shown that, for crystals with phase transition temperatures T _c < 300 K, the temperature dependence of the hysteresis loop exhibits a behavior typical of crystals with second-order phase transitions. The crystals with phase transition temperatures T _c > 300 K are characterized by double hysteresis loops in the temperature range T _c ?T ₁ ≈ 30 K. The correlation between the polarization properties and possible structural transformations of the Li_2?x Na _x Ge₄O₉ crystals due to the change in the concentration ratio of Na and Li ions is discussed.