Papers by Keyword: Rare Earth Compounds

Abstract: We report on photoluminescence (PL) properties of europium (Eu) and ytterbium (Yb) co-doped silicon oxide films with different Si excess. After annealing the films in N₂, strong PL were observed from Eu and Yb³⁺ ions and their intensities are correlated. The PL intensity of Eu is mainly from 3+ for no and relatively low temperature anneals (<900 ^°C) while the Eu²⁺ emission is dominating for annealing at 1000 ^°C or above in the co-doped Si-rich oxide films. Transmission electron microscopy shows amorphous (Eu, Yb, Si, O)-containing precipitates in the Si-rich oxide during 1000-1200 ^°C annealing and these precipitates are considered to be responsible for the Eu²⁺-related luminescence.

Abstract: The structural properties of GdFe_2-xT_x (T=Ti, Al) and their hydrides are studied by using inter-atomic potentials based on Chens lattice inversion technique. The results show that GdFe_2-xAl_x crystallizes with the MgZn₂ type phase in the range 0.35x0.7. And GdFe2-xTix crystallizes with the MgZn₂ type phase has the lowest energy for 0x<0.17 and="" the="" tolerance="" is="" acceptable="" gdfe="" sub="">2-xTi_x compounds are stabilized in MgZn₂ type phase with different Ti atoms content in the range 0.17<x0.6. Moreover, the calculated lattice constants coincide quite well with experimental values. All the results indicate the potentials are valid for studying the structural properties of the intermetallics.

Abstract: The crystalline electric field parameters A_nm for HoFe₁₁Ti under different pressures were evaluated by fitting calculations to the magnetization curves measured on the single crystals at several temperatures. It was found that magneto-crystalline anisotropy has been changed by high pressure and the A_nm for HoFe₁₁Ti under high pressures are strikingly different from A_nm for the corresponding HoFe₁₁Ti H with interstitial hydrogen atom.

Abstract: The class of R₂PdSi₃ single crystals (R= rare earth element) with hexagonal AlB₂-type crystallographic structure reveals the systematic dependence of anisotropic magnetic properties governed by the interplay of crystal-electric field effects and magnetic two-ion interactions. Here we compare the floating zone (FZ) crystal growth with radiation heating of compounds Pr₂PdSi₃ and Nd₂PdSi₃. The congruent melting behavior enabled moderate growth velocities of 3 to 5 mmh^-1. The preferred growth directions are close to the basal plane of the hexagonal unit cell. The composition of the crystals, is slightly Pd-depleted with respect to the nominal composition 16.7 at.% Pd. The Pr₂PdSi₃ compound exhibit antiferromagnetic order below the Néel temperatures T_N: 2.17 K and Nd₂PdSi₃ compound order ferromagnetically below the Curie temperature T_C = 15.1 K.

Abstract: La_1-xSr_xMnO₃ (LSMO) has recently shown promising features as a metal-insulator material over a limited range of Sr doping (x=0.175 to 0.25). Its thermal property has been commonly measured through the very expensive calorimetric method. In this paper, a considerably more convenient thermal investigation approach to this issue through the thermal irradiation theory is proposed. LSMO compounds were synthesized with a wide range of x (0.15 to 0.5) using the precisely controlled Pechini sol-gel method. XRD phase structure analysis and XPS composition and chemical state study were adopted for quality assurance of the compounds. Resistance and infrared reflectance of the samples were measured respectively with the help of the four probe technique in temperature range of 150K to 380K and an infrared spectrometer over a temperature range of 153 K to 544 K. Investigations showed a good correlation between these two measures approving the metal-insulator characteristic of all the samples. Calculation of the total normal emittance (ε_N(T)) of the compounds was innovatively simplified using the measured reflectivity data through the thermal irradiation theory for graybody. Moreover, the results showed that every x ratio fabricated through the precisely controlled Pechini method presented a unique ε_N(T) characteristic with a different metal-insulator transition temperature.

Abstract: All studied Gd_1-xCe_xIn₃ compounds crystallize in the cubic AuCu₃ - type of crystal structure. The influence of Gd/Ce substitution is reflected in the linear increase of the unit cell parameter. The temperature dependence of the electrical resistivity ρ(T) strongly depends on the Ce content. For compounds with x≤0.2 a typical metallic behavior has been observed. In contrary, for Ce-rich compounds (x≥0.5) a characteristic Kondo-type behaviour has been noticed. The analysis of cerium XPS core level lines reveals the occurrence of possible Ce intermediate valence.

Abstract: The effect of overheating treatment on the crystal orientation of the Tb0.27Dy0.73Fe1.9 alloy was investigated. The results indicated that different overheating treatment conditions could obtain different crystal orientation. It means that overheating treatment affects the process of Tb0.27Dy0.73Fe1.9 solidification. The conjectural discussions of these results are also presented.

Abstract: The compound Dy₂Si₂O₇ exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy₂Si₂O₇ are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (T_o) and density of states at fermi level are obtained. The ac conductivity σ_ac (ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σ_ac (ω) =B ω ^s , where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

Abstract: The longitudinal ultrasonic velocity (V) and attenuation at a frequency of 10MHz have been measured in single-phase polycrystalline La1/3Sr2/3Fe0.95Co0.05O3 from 20K to 300K. The temperature dependence of resistivity indicates that La1/3Sr2/3Fe0.95Co0.05O3 undergoes charge ordering transition at TCO. A dramatic increase in V is observed at TCO, which is accompanied by a sharp peak in attenuation. This simultaneous occurrence of resistivity and ultrasonic anomalous features implies extremely strong electron-phonon interaction, which is due to the the Jahn-Teller effect of high-spin Fe4+. Below TCO, another softening in V accompanied by a wide ultrasonic attenuation peak is observed. The analysis of the results suggests that these anomalies may correspond to the breathing-type distortion of Fe-O octahedron.

Abstract: The paper presents selected magnetic properties of the Gd1-xTbxNi3 intermetallic compounds. Based on the wide-ranging SQUID magnetometer (Quantum Design MPMS, temperature from 1.9K to 300K and magnetic field up to 7T) series of different magnetic measurements were carried out. In studied system the saturation magnetization and the Curie temperature strongly depends of Tb concentration. Moreover, the so-called field cooling - zero field cooling (FC-ZFC) curves reveal a dependence of M(T) on the applied magnetic field. The thermomagnetic curves indicate interesting behaviour which is typical for terbium compounds and can be ascribed to the interaction between different aligned magnetic subblattices.