scholarly journals Structural defects of rare-earth disilicides and digermanides

2020 ◽  
Vol 13 (1/2) ◽  
pp. 36-44
Author(s):  
Svitlana PUKAS ◽  
◽  
Roman GLADYSHEVSKII ◽  
Keyword(s):  
Rare Earth ◽  
Structural Defects

Isotope Exchange between 18O2 Gas and Mechanoactivated Oxides of the Family Rare Earth – Manganese – Oxygen

2014 ◽  
Vol 354 ◽  
pp. 153-158
Author(s):  
Anatoly Yakovlevich Fishman ◽  
G.A. Kozhina ◽  
Tatiana Eugenievna Kurennykh ◽  
E.V. Vykhodets ◽  
Vladimir Borisovich Vykhodets
Keyword(s):  
Rare Earth ◽  
Diffusion Coefficients ◽  
Low Temperatures ◽  
Isotope Exchange ◽  
Average Concentration ◽  
Structural Defects ◽  
Diffusion Activation Energy ◽  
Gaseous Oxygen ◽  
Oxygen Isotope Exchange ◽  
O Isotope

The results of measurements of the bulk diffusion of tracer oxygen atoms in the oxides LnMnO3+δ (Ln = La, Nd, Sm) in the temperature range 400 – 750°С are presented. The measurements were carried out on micro-and nanopowders. Nanoscale powders were prepared by mechanical activation. A method based on the study of the kinetics of oxygen isotope exchange between the powder and gaseous oxygen enriched with 18O isotope was used to obtain data on the diffusion coefficients. The average concentration of 18O isotope in the powders was measured using NRA technique. The obtained diffusion coefficients lay in the range of 10-21 - 10-24 m2/s, the diffusion activation energy for all the oxides have been close to 1 eV. These results suggest that the migration of tracer oxygen in oxides LаMnO3+δ, NdMnO3+δ and SmMnO3+δ at low temperatures is realized via structural defects. As for the oxide LaMnO3+δ, its oxygen diffusion coefficients at low temperatures have been lower than the values extrapolated from high temperatures. Such behavior of diffusion properties has not been previously observed in other metal oxides. In this regard, the vacancy formation energy in the rare earth manganites has been supposed to increase with decreasing temperature.

scholarly journals Investigation of H Sorption and Corrosion Properties of Sm2MnxNi7−x (0 ≤ x < 0.5) Intermetallic Compounds Forming Reversible Hydrides

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3470
Author(s):  
Nicolas Madern ◽  
Véronique Charbonnier ◽  
Judith Monnier ◽  
Junxian Zhang ◽  
Valérie Paul-Boncour ◽  
...  
Keyword(s):  
Rare Earth ◽  
Intermetallic Compounds ◽  
Magnetic Measurements ◽  
Energy Transition ◽  
Reversible Capacity ◽  
Binary Compound ◽  
Structural Defects ◽  
Crystallographic Axis ◽  
Corrosion Properties ◽  
Practical Applications

Intermetallic compounds are key materials for energy transition as they form reversible hydrides that can be used for solid state hydrogen storage or as anodes in batteries. ABy compounds (A = Rare Earth (RE); B = transition metal; 2 < y < 5) are good candidates to fulfill the required properties for practical applications. They can be described as stacking of [AB5] and [AB2] sub-units along the c crystallographic axis. The latter sub-unit brings a larger capacity, while the former one provides a better cycling stability. However, ABy binaries do not show good enough properties for applications. Upon hydrogenation, they exhibit multiplateau behavior and poor reversibility, attributed to H-induced amorphization. These drawbacks can be overcome by chemical substitutions on the A and/or the B sites leading to stabilized reversible hydrides. The present work focuses on the pseudo-binary Sm2MnxNi7−x system (0 ≤ x < 0.5). The structural, thermodynamic and corrosion properties are analyzed and interpreted by means of X-ray diffraction, chemical analysis, scanning electron microscopy, thermogravimetric analysis and magnetic measurements. Unexpected cell parameter variations are reported and interpreted regarding possible formation of structural defects and uneven Mn distribution within the Ni sublattice. Reversible capacity is improved for x > 0.3 leading to larger and flatter isotherm curves, allowing for reversible capacity >1.4 wt %. Regarding corrosion, the binary compound corrodes in alkaline medium to form rare earth hydroxide and nanoporous nickel. As for the Mn-substituted compounds, a new corrosion product is formed in addition to those above mentioned, as manganese initiates a sacrificial anode mechanism taking place at the early corrosion stage.

Processing of rare earth doped GaN with ion beams

2003 ◽  
Vol 798 ◽  
Author(s):  
K. Lorenz ◽  
U. Wahl ◽  
E. Alves ◽  
T. Wojtowicz ◽  
P. Ruterana ◽  
...  
Keyword(s):  
Rare Earth ◽  
Room Temperature ◽  
Lattice Site ◽  
Rutherford Backscattering Spectrometry ◽  
Structural Defects ◽  
Site Location ◽  
Transmission Electron ◽  
Infra Red ◽  
Optical Activation ◽  
Rare Earth Doped

ABSTRACTGaN epilayers grown by MOCVD were implanted with different fluences of thulium at room temperature and at 500 °C in order to find the optimum implantation conditions. Rutherford backscattering spectrometry in the channeling mode was used to monitor the damage evolution in the Ga-sublattice and to establish the lattice site location of the thulium ions. The nature of structural defects was studied with transmission electron microscopy and the optical properties of the samples with room temperature cathodoluminescence. The introduced damage could be significantly reduced by implantation at high temperature for fluences up to 5×1015 Tm/cm2. Annealing was necessary for optical activation of the implanted samples, in all cases. After annealing, sharp rare earth related emissions were observed in the blue and in the near infra-red spectral region.

Characterization of Rare-Earth Fluoride Anti-Stokes Phosphors by Scanning arid Transmission Electron Microscopy

1971 ◽  
Vol 29 ◽  
pp. 142-143
Author(s):  
N. M. P. Low ◽  
L. E. Brosselard
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Elevated Temperatures ◽  
Stoichiometric Composition ◽  
Rare Earth Ions ◽  
Crystalline Solid ◽  
Precipitation Process ◽  
Rare Earth Fluoride ◽  
Earth Fluoride ◽  
Rare Earth Fluorides

There has been considerable interest over the past several years in materials capable of converting infrared radiation to visible light by means of sequential excitation in two or more steps. Several rare-earth trifluorides (LaF3, YF3, GdF3, and LuF3) containing a small amount of other trivalent rare-earth ions (Yb3+ and Er3+, or Ho3+, or Tm3+) have been found to exhibit such phenomenon. The methods of preparation of these rare-earth fluorides in the crystalline solid form generally involve a co-precipitation process and a subsequent solid state reaction at elevated temperatures. This investigation was undertaken to examine the morphological features of both the precipitated and the thermally treated fluoride powders by both transmission and scanning electron microscopy.Rare-earth oxides of stoichiometric composition were dissolved in nitric acid and the mixed rare-earth fluoride was then coprecipitated out as fine granules by the addition of excess hydrofluoric acid. The precipitated rare-earth fluorides were washed with water, separated from the aqueous solution, and oven-dried.

Transmission electron microscopy of composite materials

1988 ◽  
Vol 46 ◽  
pp. 1012-1015
Author(s):  
K.P.D. Lagerlof
Keyword(s):  
Composite Materials ◽  
Physical Properties ◽  
Structural Defects ◽  
Structural Composites ◽  
Multiphase Materials ◽  
Structural Reinforcement ◽  
Transmission Electron ◽  
Reinforced Fiber ◽  
Particulate Reinforced Composites ◽  
Definition Of

Although most materials contain more than one phase, and thus are multiphase materials, the definition of composite materials is commonly used to describe those materials containing more than one phase deliberately added to obtain certain desired physical properties. Composite materials are often classified according to their application, i.e. structural composites and electronic composites, but may also be classified according to the type of compounds making up the composite, i.e. metal/ceramic, ceramic/ceramie and metal/semiconductor composites. For structural composites it is also common to refer to the type of structural reinforcement; whisker-reinforced, fiber-reinforced, or particulate reinforced composites [1-4].For all types of composite materials, it is of fundamental importance to understand the relationship between the microstructure and the observed physical properties, and it is therefore vital to properly characterize the microstructure. The interfaces separating the different phases comprising the composite are of particular interest to understand. In structural composites the interface is often the weakest part, where fracture will nucleate, and in electronic composites structural defects at or near the interface will affect the critical electronic properties.

Study of segregation in La1.8Sr0.2CuO4 superconductor by STEM-EDS microanalysis

1987 ◽  
Vol 45 ◽  
pp. 54-55
Author(s):  
T. F. Kelly ◽  
P. J. Lee ◽  
E. E. Hellstrom ◽  
D. C. Larbalestier
Keyword(s):  
Rare Earth ◽  
High Field ◽  
Transport Current ◽  
Total Thickness ◽  
New Class ◽  
Ceramic Superconductors ◽  
Current Densities ◽  
Group Ii ◽  
Eds Microanalysis

Recently there has been much excitement over a new class of high Tc (>30 K) ceramic superconductors of the form A1-xBxCuO4-x, where A is a rare earth and B is from Group II. Unfortunately these materials have only been able to support small transport current densities 1-10 A/cm2. It is very desirable to increase these values by 2 to 3 orders of magnitude for useful high field applications. The reason for these small transport currents is as yet unknown. Evidence has, however, been presented for superconducting clusters on a 50-100 nm scale and on a 1-3 μm scale. We therefore planned a detailed TEM and STEM microanalysis study in order to see whether any evidence for the clusters could be seen.A La1.8Sr0.2Cu04 pellet was cut into 1 mm thick slices from which 3 mm discs were cut. The discs were subsequently mechanically ground to 100 μm total thickness and dimpled to 20 μm thickness at the center.

High-angle electron scattering from amorphous silicon

1995 ◽  
Vol 53 ◽  
pp. 162-163
Author(s):  
M. Libera ◽  
J.A. Ott ◽  
K. Siangchaew ◽  
L. Tsung
Keyword(s):  
Electron Scattering ◽  
Amorphous Material ◽  
Structural Defects ◽  
Constant Thickness ◽  
High Angle ◽  
Fast Electrons ◽  
Angle Scattering ◽  
Stem Image ◽  
Amorphous Si ◽  
Thermal Vibrations

Channeling occurs when fast electrons follow atomic strings in a crystal where there is a minimum in the potential energy (1). Channeling has a strong effect on high-angle scattering. Deviations in atomic position along a channel due to structural defects or thermal vibrations increase the probability of scattering (2-5). Since there are no extended channels in an amorphous material the question arises: for a given material with constant thickness, will the high-angle scattering be higher from a crystal or a glass?Figure la shows a HAADF STEM image collected using a Philips CM20 FEG TEM/STEM with inner and outer collection angles of 35mrad and lOOmrad. The specimen (6) was a cross section of singlecrystal Si containing: amorphous Si (region A), defective Si containing many stacking faults (B), two coherent Ge layers (CI; C2), and a contamination layer (D). CBED patterns (fig. lb), PEELS spectra, and HAADF signals (fig. lc) were collected at 106K and 300K along the indicated line.

Sign in / Sign up

Export Citation Format

Share Document