Diffusion Of Nd Research Articles

Extraction and recovery of rare earth elements from NdFeB waste using bismuth reinforced by supergravity

NdFeB stands as the foremost utilized material in permanent magnet applications, generating substantial quantities of NdFeB magnet waste annually. These wastes contain 20−30 wt. % rare earth elements (REEs) and are valuable secondary resources. In this paper, Bi was used as extractant to recover REEs in NdFeB waste by pyrometallurgy, and excess Bi was separated by supergravity technology for recycling. The migration and diffusion behaviors of REEs during the extraction process were investigated, with the diffusion coefficient of REEs in Bi obtained. The influence of Bi-to-waste mass ratio on rare earth extraction efficiency in smelting process, alongside the effect of temperature and gravity coefficient on the Bi recovery rate in supergravity centrifugation process were delineated. Findings revealed that the diffusion of Nd in Bi and NdFeB conformed to Fick's second law. Notably, with a Bi-to-waste mass ratio surpassing 1:1, spontaneous separation occurred between the Bi and Fe phases, facilitating the migration of almost all REEs from NdFeB waste into the Bi phase. Under the optimal conditions (Bi/NdFeB mass ratio of 4:3, separation temperature of 500°C and a gravity coefficient of 1000), the recovery rate of REEs during the smelting stage reached 99.6%, while the Bi recovery rate during the supergravity stage was 74.7%. Additionally, the overall REE recovery rate and Bi recovery rate during the entire process reached 99.3% and 70.3%, respectively. The successful development of this process has opened up a new way for recycling REEs from NdFeB waste.

Macro-controlling of the element distribution to prepare high-performance sintered (Nd, Dy)-Fe-B composite magnets

Two magnets prepared by dual-main-phase (Nd13Fe81B6 and Dy21Fe73B6) and single-main-phase (Nd13Fe81B6 with DyHx doping) approaches. The content of the Dy element in the composite magnet with dual-main-phase structure (6.75 wt%) is lower than that of the magnet with single-main-phase structure (7 wt%). But the dual-main-phase magnet's coercivity, remanence, and the magnetic energy product are 5.08 kOe, 0.36 kG, and 2.99 MGOe, higher than those of the single-main-phase magnet. In the dual-main-phase magnet, the diffusion of Nd and Dy elements is more prominent. Part Dy element replaces the Nd element to form (Nd, Dy)2Fe14B phase, and the remaining Dy element exists in the form of Dy2Fe14B phase, which improves the comprehensive magnetic performance of the magnet. As a result, Dy element in the dual-main-phase magnet is fully utilized. In the single-main-phase magnet, the Dy element replaces the Nd element to form the (Nd, Dy)2Fe14B phase. However, the remaining non-magnetic Dy element from DyHx concentrates in the grain boundary, it reduces the magnetic properties of magnets and leads to the waste of Dy elements. The results show that the dual-main-phase structure can control the diffusion of Nd and Dy elements, optimize the distribution of Dy elements, effectively increase the utilization rate of Dy elements and improve the comprehensive magnetic properties of sintered magnets.

Reaction mechanism of Ca-reduction diffusion process used for sustainable recycling Nd-Fe-B sludge

The reduction diffusion (RD) process for Nd-Fe-B sludge has been reported as a green and efficient method for synthesizing recycled Nd2Fe14B magnetic powders. In this work, recycled Nd-Fe-B powders with low impurity content and uniform particle size distribution were successfully prepared. M3 T increased to 146.25 emu/g, which was about 17% and 32% higher than the purged and original sludge, respectively. Then, the recycled Nd-Fe-B sintered magnets with properties of Br = 12.14 kG, Hcj = 12.00 kOe, and (BH)m = 35.05 MGOe were successfully prepared by doping with 37.70 wt% Nd4Fe14B powders. Based on experimental studies of calcium thermal reduction of Nd-Fe-B sludge and thermo-kinetic analysis, the reaction mechanism of the RD method for sludge waste recovery was clarified. In the RD process, the oxides in the sludge were selectively reduced by Ca at 600–950 °C and the reduced Nd diffused to the surface of the Fe core, forming the Nd-Fe-B alloy, where the formation process included the nucleation stage, the alloy layer high-speed growth stage, and the completion stage. And the relationship between the alloy layer thickness and time during the high-speed growth period of 1–3 h was more in line with linear law (d = 5.41 t–4.31). The RD reaction conformed to the unreacted shrinking core model, and its reaction rate control step consisted of a one-way diffusion process for the diffusion of Nd into the Fe core.

The influence of Gallium doping on the magnetic performance and microstructure of Nd-Fe-B sintered magnets

The influence of Gallium (Ga) doping on the microstructure, thermal stability and the magnetic properties of Nd-Fe-B based sintered magnets was investigated in this paper. It is shown that the intrinsic coercivity increases significantly from 12.4 kOe to 19.4 kOe while the remanence decreases slightly from 14.03 kGs to 13.70 kGs when Ga content increases from 0.0 wt% to 0.5 wt%. The thermal stability of the Ga-doped sample is much better than that of Ga-free sample. Temperature coefficient of intrinsic coercivity β @ 20-120 ℃ by doping 0.5 wt% Ga is −0.585 %/K, which is better than that of Ga-free sample (-0.622%/K). It was observed by the microstructures that the addition of Ga can promote the diffusion of Nd and Cu from triple junction phase (TJP) into grain boundary phase while Fe atoms are enriched around TJPs, resulting in continuous grain boundary (GB) phase and reducing the Fe concentration in GB phase. The Curie temperature increases from 583 K to 585 K after doping 0.5 wt% Ga.

Bulk and surface diffusion of neodymium in alpha-uranium: Ab initio calculations and kinetic Monte Carlo simulations

• A Nd interstitial is found to be intrinsically unstable in alpha- U . • The binding between the substitutional Nd and the U vacancy in strong in alpha- U . • Nd atoms migrate in bulk alpha- U via the vacancy mechanism. • Radiation can significantly accelerate the bulk diffusivity of Nd in alpha- U . • Diffusion of Nd adatoms via pore surfaces is much faster than bulk diffusion. A fundamental understanding of lanthanide transport in metallic fuels is critical for high fidelity modeling of the fuel-cladding chemical interaction (FCCI) phenomenon, which can lead to the formation of brittle intermetallic compounds and premature failure of the cladding. Here we report a combined ab initio density functional theory (DFT) and kinetic Monte Carlo (KMC) study of the bulk diffusivity of Nd in α-U , fully taking into account the effect of radiation enhanced diffusion. The vacancy mechanism is considered to be the dominant mechanism for the bulk diffusion of Nd since a Nd interstitial is found to be intrinsically unstable in α-U . The surface diffusivity of a Nd adatom on α-U (001) surface has been further predicted using KMC simulations parameterized by DFT calculations. The present study suggests that Nd transport via the surface diffusion mechanism can be many orders of magnitude faster than bulk diffusion. Furthermore, the results from the present lower length scale study can be used to inform mesoscale phase-field simulations to determine the effective diffusion coefficient of Nd through α-U with a porous microstructure.

Accommodation and diffusion of Nd in uranium silicide - U3Si2

Uranium silicide, U3Si2, is considered as an advanced nuclear fuel for commercial light water reactors with improved accident tolerance as well as competitive economics. Nd is employed as a local burnup indicator for conventional oxide fuels due, among other reasons, to its low mobility in the UO2 fuel matrix and its high fission product yield. As part of the studies necessary to determine whether Nd can be considered as a candidate burnup indicator in the U3Si2 concept fuel, we investigate the mobility of Nd in U3Si2. In this work, density functional theory (DFT) calculations are performed to predict the most stable accommodation sites of Nd in U3Si2, found to be within the uranium sublattice. Based on DFT calculations of binding energies and migration activation energies, we investigate Nd diffusion by computing the transport coefficients within the framework of the self-consistent mean-field method. Our calculations predict that the diffusion ratio of Nd to U is smaller in U3Si2 than in UO2. Moreover, at the individual maximum centerline temperature of the fuel, the diffusion of Nd in U3Si2 is much slower than in UO2. From this perspective, Nd represents a good candidate burnup indicator, in similarity to that in UO2.

Effects of (Nd, Pr)-Hx addition on the coercivity of Nd-Ce-Y-Fe-B sintered magnet

Y-Ce co-substituted RE-Fe-B (RE, rare earth) sintered magnets with good thermal stability have attracted growing attention as low-cost hard magnetic materials. The inferior intrinsic properties of Y2Fe14B and Ce2Fe14B to Nd2Fe14B, however, limit the substitution of Y-Ce for Nd at a low level. In this work, (Nd, Pr)-Hx powders are introduced into (Nd, Pr)22.8(Y, Ce)7.7FebalM1.3B1.0 sintered magnets to further enhance the coercivity. By incorporating 1 wt% (Nd, Pr)-Hx, the coercivity is increased to 9.7 kOe, which is 16.9% higher than that for the starting magnet (8.3 kOe). Continually increasing (Nd, Pr)-Hx addition to 2 and 3 wt% lead to a very limited coercivity increment, i.e. to 10.0 kOe and 10.3 kOe, respectively. The formation of continuous RE-rich intergranular phase by the extra Nd/Pr after (Nd, Pr)-Hx dehydrogenation can enhance the magnetic isolation effect between adjacent matrix phase grains, resulting in coercivity enhancement. However, more Nd atoms exist in the RE-rich phase rather than form the Nd-rich hardening shell, which is distinct from the available Nd-Ce-Fe-B system. The REs distribution within the matrix phase grain is similar before and after (Nd, Pr)-Hx incorporation for the Nd-Ce-Y-Fe-B system. It is deemed that the preferential occupancy of Y in the 2:14:1 matrix phase hinders the diffusion of Nd into the outer layer of Y-Ce enriched regions, being responsible for the limited coercivity increment with higher (Nd, Pr)-Hx addition. The present work suggests that tuning the distribution of Y is of crucial importance to further improve the coercivity of Y-containing permanent magnets.

Manufacturing of Die-Upset Rare Earth–Iron–Boron Magnets With (Ce,La)-Mischmetal

Utilization of the relatively abundant and inexpensive (Ce,La)-mischmetal in manufacturing die-upset R-Fe-B magnets (R = rare earth) from melt-spun nanocrystalline alloys was attempted via: 1) the standard single-alloy process; 2) the diffusion of Nd and Pr from low-melting-temperature alloys blended into the magnet; and 3) the diffusion of Nd and Pr by infiltrating the magnet through its surface. No practically viable magnetic properties could be obtained without the introduction of Nd(Pr). Blending with the (Nd,Pr)-rich alloys was found to be less efficient for the development of coercivity than the single-alloy process; so was the infiltration of those precursors which had been alloyed with 0.5 at.% Ga. More efficient than the single-alloy process was infiltration of those precursors which had been alloyed with 2 at.% Si or with 1 at.% Zn. Coercivities of 7-10 kOe and energy products of 17-20 MGOe were obtained for magnets having 43%-55% of the R elements represented by Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> and containing overall 7.5-9.7 at.% Nd(Pr). The coercivity of the significantly hyper-stoichiometric (17-19 at.% R) (Ce,La)-containing alloys was found to decline 80% or more as a result of the deformation process, but partially recover after subsequent annealing. The latter improvement is likely to be caused by redistribution of the R-rich phases.

Enhanced coercivity of Nd-Ce-Fe-B sintered magnets by adding (Nd, Pr)-H powders

Incorporating the highly abundant rare earth (RE) Ce into Nd-Fe-B sintered magnets has attracted considerable interest recently. The inferior anisotropic field (HA) of Ce2Fe14B to Nd2Fe14B, however leads to low coercivity of the Nd-Ce-Fe-B magnets. To further enhance the coercivity, in this work, (Nd, Pr)-H powders were used as intergranular additive to restructure the grain boundaries of the low cost (Nd,Pr)22.3Ce8.24FebalB1 (wt.%) sintered magnets. When added with only 2 wt% (Nd, Pr)-H, the Hcj can be enhanced from 10.6 kOe to 12.7 kOe with slight reduction in remanence and maximum energy product. The dehydrogenation of (Nd, Pr)-H during sintering promotes the diffusion of Nd and Pr towards the 2:14:1 phase grains and the smoothing of grain boundaries. The formation of (Nd, Pr)-rich shell with locally enhanced magnetocrystalline anisotropy and the magnetic isolation between adjacent 2:14:1 phase grains result in obvious coercivity enhancement, which was supported by magnetic domain structure characterizations and micromagnetic simulations. It suggests that through grain boundary restructuring, the coercivity of Nd-Ce-Fe-B magnets can be enhanced to be comparable of commercial Nd-Fe-B magnets, which may shed new insights into the fabrication of low cost RE permanent magnets.

Radiation enhanced diffusion of Nd in UO2

Single crystal UO2 thin films with Nd as tracer elements in the film mid-plane have been grown on yttria-stabilized zirconia (YSZ) substrates. The films were irradiated with 1.8 MeV Kr+ ions in the temperature range from 400 °C to 1113 °C, where an evident enhanced diffusion was found in UO2. The temperature dependent measurements have shown an activation energy of 0.56±0.04 eV below 800 °C, and 1.9±0.3 eV above 900 °C. The rate-dependent measurements have shown a linear dependence on the radiation flux, which indicates radiation enhanced diffusion (RED) is in the sink limited kinetics regime. Comparison of the RED results between UO2 and CeO2 has shown significant differences, which indicates that CeO2 used as UO2 surrogate may be questioned in terms of cation diffusion.

Diffusion of Nd and Mo in lanthanum tungsten oxide

Cation diffusion in functional oxides exposed to electrochemical gradients may lead to kinetic demixing or decomposition and, consequently, determine the life-time of the functional component. Here we present chemical diffusion coefficients of Nd and Mo in the mixed proton–electron conductor lanthanum tungsten oxide, La28−xW4+xO54+3x/2 (LWO), measured at 1000 to 1200°C in both oxidizing and reducing atmospheres. The bulk diffusivities of Nd and Mo were similar at all temperatures investigated and did not change significantly from oxidizing to reducing conditions. On these bases it is suggested that bulk diffusion of both Nd and Mo occurs via the La2 site on which both cations reside. Based on the low activation energy for bulk transport (~200kJ∙mol−1) at temperatures below 1200°C it is proposed that the cation defect concentrations are, in effect, frozen in. Preferential diffusion of Nd along the grain boundaries was rationalized based on space charge effects and depletion of W6+ and Mo6+ near the positively charged grain boundary core. Potential implications of kinetic demixing or decomposition of LWO membranes are also evaluated based on the present results.

Coercivity enhancement of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B powders by the diffusion of Nd–Cu eutectic alloys

We report the coercivity enhancement of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B nanocrystalline powders from 1321 to 1552 kA m−1 (19.5 kOe) by the grain boundary diffusion of Nd–Cu melts with hyper-eutectic compositions. A distinct Nd-rich grain boundary phase was observed after the diffusion process by scanning electron microscopy and transmission electron microscopy; however, atom probe tomography indicated that the change in composition of the grain boundary phase was not significant. The mechanism of the coercivity enhancement is discussed based on these results.

The effect of silica doping on neodymium diffusion in yttrium aluminum garnet ceramics: implications for sintering mechanisms

The Nd 3+ cation diffusion into transparent polycrystalline YAG (Y 3Al 5O 12) was investigated as a function of temperature and silica content. Thin neodymium oxide layers were deposited on sintered YAG substrates prior to annealing under air at temperatures from 1400 to 1600 °C. Bulk and grain boundary neodymium diffusion coefficients were measured by secondary ion mass spectrometry. The experimental results show that silica addition increases the diffusivity of Nd 3+ by a factor 10 whatever the diffusion path, probably as a result of extrinsic point defects formation, especially rare-earth vacancies. The experimental diffusion data were used to elucidate the sintering mechanism of Nd:YAG ceramics in the temperature range 1450–1550 °C. Firstly, it appeared that the intermediate stage of solid-state sintering should be controlled by the rare-earth diffusion along the grain boundary with an activation energy of about 600 kJ mol −1. Secondly, grain growth mechanism at the final stage of liquid-phase sintering was investigated for silica-doped Nd:YAG samples. Thus, the grain growth should be limited by the reaction at interfaces at a temperature lower than 1500 °C, with an activation energy of about 880 kJ mol −1. At higher temperature, it seems to be limited by the ionic diffusion through the intergranular liquid phase, with an activation energy of 250 kJ mol −1.

Individualization of textural and reactional microdomains in eclogites from the Bergen Arcs (Norway): Consequences for Rb/Sr and Ar/Ar radiochronometer behavior during polymetamorphism

Rb/Sr, 40Ar/39Ar, and Sm/Nd isotopic data are reported in Caledonian eclogites from the Lindås Nappe, Bergen Arcs, Norway, in order to investigate processes controlling isotopic equilibrium at mineral scale in polymetamorphic rocks. The Bergen Arcs exposes Sveconorwegian ∼950–930 Ma granulites, partially overprinted by Caledonian eclogite‐facies metamorphism at ∼425 Ma and amphibolite‐facies metamorphism at ∼410 Ma. Geochemical and Rb‐Sr data from more than 10 phengite fractions separated from one sample reflect the composition of the microdomain (a few hundred microns in size) in which phengite crystallized. Phengite crystallized after garnet or plagioclase by dissolution‐precipitation processes yield apparent age between 700 and 600 Ma. At the time of their crystallization, these phengites inherited the isotopic composition of their precursor minerals, at a microdomain scale. Phengite from quartz veins, which crystallized from elements mobilized by the circulating fluid, yield an age closer to the eclogite‐facies metamorphic age. The closed system evolution of the eclogitizing fluid, the segregation of textural and reactional microdomains, the high Sr content of the studied phengite, and the short duration of the recrystallization processes (&lt;1Ma) are interpreted as the main factors responsible for the lack of a Rb/Sr isotopic equilibrium, at the scale of hand samples. Such equilibrium is nevertheless reached in quartz veins where the crystallization of minerals implies that the fluid circulation acted as a factor of isotopic homogenization. The in situ single mineral Ar/Ar datings revealed that both eclogite‐ and amphibolite‐facies minerals are characterized by an excess of radiogenic argon (ages between 425 and 520 Ma). The excess of argon has been inherited from the previous granulite and has been only partially evacuated from the system by the circulating fluid. The apparent Sm/Nd ages from garnets inherited from the granulite‐facies metamorphism (c. 930 Ma) are in agreement with previous estimates. This result confirms that the diffusion of Nd in garnet does not occur at temperatures lower than 700°C. This study highlights the complexity of radiochronometer behavior during HP metamorphism and demonstrates that coupling different radiochronometers, such as Ar/Ar and Rb/Sr, does not always guarantee the validity of the geochronological results.

Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals

The temperature and compositional dependences of thermo-optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time-resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time-resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd:YAG ceramics. Finally, our results showed the ability of the time-resolved thermal lens to determine and optimize the thermo-optical properties of Nd:YAG ceramic based lasers.

Cation diffusion in soda-lime-silicate glass melts

Cation diffusion was experimentally investigated in soda-lime-silicate glass melts (composition in mol%: 74SiO2–16Na2O–10CaO) at temperatures from 1000 to 1200°C using the diffusion couple technique. One half of each diffusion couple was doped with 11 trace elements (500ppm by weight of Rb, Cs, Sr, Zn, Cd, Nd, Eu, In, Sn, Ge and 1000ppm by weight of Fe). Experiments were performed in an internally heated gas pressure vessel at a confining pressure of 100MPa to avoid convective fluxes in the diffusion samples. The distribution of major elements was analyzed by electron microprobe. IR spectroscopy was used to quantify concentrations of dissolved water in the run products. Trace element diffusion profiles were measured simultaneously employing synchrotron X-ray fluorescence microanalysis. In all analyzed glasses the highest diffusion coefficients were observed for Rb whereas Nd was always the slowest element, e.g. at 1000°C the diffusivity decreases from (1.51±0.35)×10−11m2/s for Rb to (1.29±0.34)×10−13m2/s for Nd. The diffusivity of Nd is close to the chemical diffusivity of network former calculated from viscosity data using the Eyring relationship. Surprisingly, the rare earth elements Nd (3+) and Eu (mixed 2+, 3+) diffuse more slowly than the tetravalent Ge. Activation energies for diffusion increase from (132.1±1.5)kJ/mol for Rb to (205±16)kJ/mol for Eu. Based on the diffusion data for Eu, Sr and Nd we estimated that Eu2+/Eutotal ratios in soda-lime-silicate glass melts are below 0.04 both at reducing and oxidizing conditions.

Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates

Volume diffusion rates for five rare earth elements (La, Ce, Nd, Dy, and Yb) have been measured in single crystals of natural diopside at pressures of 0.1 MPa to 2.5 GPa and temperatures of 1,050 to1,450 °C. Polished, pre-annealed crystals were coated with a thin film of rare earth element oxides, then held at constant temperature and pressure for times ranging from 20 to 882 h. Diffusion profiles in quenched samples were measured by SIMS (secondary ion mass spectrometry) depth profiling. At 1 atm pressure, with the oxygen fugacity controlled near the quartz–fayalite–magnetite buffer, the following Arrhenius relations were obtained for diffusion normal to (001) (diffusion coefficient D in m2/s): log10 D Yb =(–4.64±0.42)–(411±12 kJ/mol/2.303RT); log10 D Dy =(–3.31±1.44)–(461±41 kJ/mol/2.303RT); log10 D Nd =(–2.95±2.64)–(496±77 kJ/mol/2.303RT); log10 D Ce =(–4.10±1.08)–(463±31 kJ/mol/2.303RT); log10 D Lu =(–4.22±2.66)–(466±78 kJ/mol/2.303RT). Diffusion rates decrease significantly with increasing ionic radius, with La a factor of ~35 slower than Yb. The relationship between diffusivity and ionic radius is consistent with a model in which elastic strain plays a critical role in governing the motion of an ion through the crystal lattice. Activation volumes for Yb and Ce diffusion, at constant temperature and oxygen fugacity, are 9.0±2.0 cm3/mol and 8.9±3.2 cm3/mol, respectively, corresponding to an order of magnitude decrease in diffusivity as pressure is increased from 0 to 3 GPa at 1,200 °C. Diffusion of Nd is such that grain-scale isotopic equilibrium in the mantle can be achieved in ~1 My under conditions near the peridotite solidus (~1,450 °C at 2.5 GPa). The equilibration time is much longer under P, T conditions of the lithospheric mantle or at the eclogite solidus (~1 Gy at 1.5 GPa and 1,150 °C). Because of the relatively strong decrease in diffusivity with pressure (two orders of magnitude between 2.5 and 15 GPa along an adiabatic temperature gradient), Nd transport in clinopyroxene will be effectively frozen at pressures approaching the transition zone, on time scales less than 100 My. Rare earth element diffusion rates are slow enough that significant disequilibrium uptake of REE by growing clinopyroxene phenocrysts may be preserved under natural conditions of basalt crystallization. The relative abundances and spatial distributions of REE in such crystals may provide a sensitive record of the cooling and crystallization history of the host lava.

Liquid metal extraction of Nd from NdFeB magnet scrap

This research involves using molten magnesium (Mg) to remove neodymium (Nd) from NdFeB magnet scrap by diffusion. Mg was melted over pieces of NdFeB scrap and held at temperatures in the range 675–705 °C for 2–8 h. The Mg was allowed to solidify, and the castings were then sectioned and characterized using scanning electron microscopy, x-ray diffraction, and chemical analysis. Nd was found to have diffused out of the solid scrap into the molten Mg. The thickness of the diffusion layer was measured, the diffusion of Nd through the NdFeB scrap into liquid Mg was described, and the diffusion coefficient of Nd in liquid Mg was estimated.

Luminescence method for the study of Nd3+ ions diffusion in AgBr crystals

This study of diffusion of Nd in AgBr is motivated by our interest in the preparation of Nd-doped AgBr crystals that show lasing effects in the near and midinfrared. The doping can be done in several ways. We propose that monitoring the infrared luminescence along the direction of diffusion of activator ions in crystals of AgBr is a sensitive and minimally invasive method of determining the diffusion coefficient, the diffusion enthalpy, and the temperature dependence of these parameters for ions of interest. We have used this technique to study the diffusion of Nd3+ in AgBr crystals. To establish the concentration range in which the luminescence method is useful, the dependence of the luminescence kinetics on the Nd-ion concentration was investigated. The temperature dependence of the diffusion coefficient (D0=1.2×10−5 cm2/s at room temperature), and the diffusion enthalpy (H=0.51 eV) were determined. We found that high values of the diffusion coefficient and low values of the diffusion enthalpy facilitate preparation of high optical quality Nd-doped AgBr crystals. Such crystals are candidates for lasing action.

Heat diffusivity of Nd 1− xSr xMnO 3−δ compounds

The thermal diffusivity of several samples of Nd 0.67Sr 0.33MnO 3−δ was investigated in the temperature range 35 K < T < 350 K and is correlated with magnetization, resistivity and thermopower data. We find an anomaly of the heat diffusivity D T near 100 K which we attribute to a temperature-induced canted metal-afm insulator transition, a second anomaly in D T( T) and a sign change in S( T) near 350 K which we assign to the transition to paramagnetism.