Crystals Of La1 Research Articles

Structure and Optical Properties of Langasite Family Crystals (La1–xNdx)3Ga5SiO14 (x = 0, 0.4, 0.6, 1)

Structure and Optical Properties of Langasite Family Crystals (La1–xNdx)3Ga5SiO14 (x = 0, 0.4, 0.6, 1)

Electron diffraction study and ionic conductivity of fluorite Ba1-xLaxF2+x and tysonite La1-yBayF3-y phases in the BaF2-LaF3 system

Crystals of fluorite phases with the CaF2 structure: Ba1−xLaxF2+x (x = 0, 0.05, 0.105, 0.25, 0.35, 0.40) and those of tysonite ones with the LaF3 structure: La1−yBayF3−y (y = 0, 0.05, 0.09) have been studied by electron diffraction and elemental analysis in a transmission electron microscope. Diffraction patterns of Ba1−xLaxF2+x crystals with x = 0.105, 0.25 exhibit diffuse scattering, which indicates the presence of clusters of structural defects. Blurred supercell reflections are seen in diffraction patterns of Ba1−xLaxF2+x crystals with a high lanthanum content (x = 0.35, 0.40) in addition to diffuse scattering. They indicate the existence of nanoscale ordered crystallites as well as clusters. It was found that LaF3 and the tysonite phase La1−yBayF3−y with a low barium content (y = 0.05) is of a low-temperature l-form (space group P3¯c1, Z = 6). A small fraction of tysonite crystallites in La1-yBayF3-y crystals with y = 0.09 is of a high-temperature h-form (space group P63/mmc, Z = 2). An intermediate crystal structure between l- and h-forms was also found.The maximum ionic conductivity σdc of tysonite crystals La1−yBayF3−y at 293 K is 800 times higher than that of fluorite ones Ba1−xLaxF2+x. A correlation was found between logarithm of conductivity and composition: lg σdc(x) = ax + b for fluorite Ba1−xLaxF2+x and tysonite La1−yBayF3−y crystals. The reason for the additive law of change in ionic conductivity in both types of nonstoichiometric phases in the BaF2-LaF3 system is apparently the similarity of defect structures of fluorite and tysonite phases.

Ultrafast Jahn–Teller polaron dynamics in a bi‐layered manganite single crystal

We report the photoinduced ultrafast quasiparticle recombination dynamics of colossal magnetoresistance single crystal La1.2Sr1.8Mn2O7 by using femtosecond time‐resolved reflection spectroscopy in a wide range of temperatures. Here, we find the transient reflectivity change ΔR exhibits a competition process of a fast negative component (∼ sub‐picosecond) against a slow positive component (∼ nanosecond), as the sample goes from paramagnetic (PM) to ferromagnetic (FM) state with decreasing the temperature. The very fast initial decay of the photoinduced ΔR corresponds to the photoionization of the Jahn–Teller polaronic response, which is unambiguously sensitive to the coupling between electron and lattice in the PM and FM phases in La1.2Sr1.8Mn2O7 single crystal. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Memory Effects in the Charge Response of Lightly Doped La2−x Sr x CuO4

The in-plane magnetoresistance (MR) of a single crystal La1.97Sr0.03CuO4 has been studied at low temperatures T using several experimental protocols. At T well below the spin-glass transition temperature, the MR becomes positive and exhibits several glassy features, such as history dependence, memory, and hysteresis. These observations are qualitatively similar to the previously reported behavior of the out-of-plane resistance. The results suggest that the memory effects in the MR are related to the onset of glassiness in the dynamics of doped holes.

Electrical conductivity of γ-irradiated crystals of La0.95Ba0.05F2.95 superionic conductor

The electrical conductivity of single crystals of the La0.95Ba0.05F2.95 superionic conductor subjected to irradiation by γ quanta (source γ-60Co, dose 2 × 106 rad) has been investigated. It is shown that the radiation defects do not have a great effect on the ionic conductivity of nonstoichiometric La0.95Ba0.05F2.95 crystals, which is caused by the heterovalent replacements of La3+ cations with Ba2+ cations.

Correlation between the nucleation of a Griffiths-like Phase and Colossal Magnetoresistance across the compositional metal-insulator boundary in La1-xCaxMnO3

Detailed measurements of the magnetic and transport properties of single crystals La1−xCaxMnO3 (0.18 ≤ x ≤ 0.27) are summarized; comparisons between which (i) not only confirm that Griffiths Phase-like(GP) features are not a prerequisite for CMR, but also demonstrate that the presence of GP-like characteristics do not guarantee the appearance of CMR; (ii) indicate that whereas continuous magnetic transitions occur for 0.18 ≤ x ≤ 0.25, the universality class of these transitions belongs to that of nearest-neighbour 3D Heisenberg model only for x ≤ 0.20, beyond which complications due to GP-like behaviour occur.

Anomalous temperature dependence of the magnetization in La0.84Sr0.16MnO3

The superconducting quantum interference device (SQUID) magnetization measurements have been performed on single crystal manganites La1−xSrxMnO3 (x=0.16;0.17) previously studied by the NMR method. For the x=0.16 sample an anomaly in the temperature dependence of the saturation magnetization at T1≈130 K is observed, which manifests itself as a cusp in dm/dT. This temperature lying well below the metal-insulator transition at TMI=157 K seems to correspond to an orbital ordering temperature Too indicated also by the decrease in the low field FC susceptibility. The observed anomaly, which is also reproduced in the temperature dependence of the NMR frequency, is ascribed to a continual decrease in the exchange interaction within the temperature interval 60 K and the difference between TMI and Too to an inherent inhomogeneity in Sr concentration. The relative SQUID magnetizations are compared with the NMR values.

Effect of Temperature on La<sub>1.85</sub>Sr<sub>0.15</sub>CuO<sub>4</sub> Single Crystal Growth by Floating Zone Method

Superconducting single crystals of La1.85Sr0.15CuO4 have been grown at various temperatures without single crystal seeds by the traveling-solvent floating-zone method. In order to avoid the formation of bubbles during the crystal growth process, a flowing atmosphere of 2 atm oxygen or 1 atm air was applied in different temperature range. It was found that the crystal quality could be improved by raising the growth temperature in a certain range, and the orientation changed from (110) to (100) at higher temperature. X-ray diffraction results showed that the full-width at half-maximum of the best as-prepared crystal was 0.086°. The crystals grown in 2 atm oxygen showed a superconducting transition temperature (Tc) of 37.3 K, while the crystals grown in floating air showed a Tc of about 35 K and it could be improved to 36.5 K by annealing in flowing oxygen.

Defects in doped perovskite-like lanthanum cobaltite crystals La1−x SrxCo1−y MeyO3−δ (Me = Cu and Mn)

The paper presents a thermodynamic analysis of the formation of equilibrium defects in perovskitelike La1−xSrxCo1−yMeyO3−δ oxides, where Me = Cu or Mn, x = 0.0 or 0.3, and y = 0.0, 0.25, or 0.3, at high temperatures (873 K ≤ T ≤ 1373 K) depending on the composition and oxygen pressure (10−8 atm ≤ \(p_{O_2 } \) ≤ 1 atm). The results were used to study the nature of charge transfer. Small-radius polarons were shown to be responsible for the electric properties of the cobaltites under consideration; their concentrations and mobilities were calculated.

Floating zone growth and magnetic and specific heat properties of La 0.67 Ca 0.33 Mn 1− x Fe x O 3 ( x =0.00, 0.04) single crystals

Single crystals of La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3 were obtained by floating zone method. Laue diffraction pattern and rocking curve of the single crystals show that their quality is good. The magnetic behaviours of these compounds have been studied. Fe doping significantly depresses the magnetic contribution to the total specific heat C-P, but slightly influences the lattice contribution at temperatures above 50K. The peak of C-P, shifts towards high temperatures with increasing magnetic field. Both single crystals exhibit the first-order magnetic transition around the Curie temperature.

Crystal structure of dilanthanum tris(monohydrogenphosphate(III)), La2(HPO3)3

H3La2O9P3, orthorhombic, Pnma (no. 62), a = 8.305(2) A, b = 14.579(3) A, c = 7.059(1) A, V = 854.7 A, Z = 4, Rgt(F) = 0.042, wRref(F) = 0.069, T = 295 K. Source of material Crystals of the title compound were obtained by hydrothermal treatment of a mixture of lanthanum hydroxide, boron sesquioxide and sodium hypophosphite monohydrate in a Teflon autoclave (V= 20ml) at 443K. 0.750 g (3.949mmol)La(OH)3, 0.562 g (8.072mmol) B2O3 and 1.712 g (16.152mmol) NaH2PO2 · H2O were intensively mixed by grinding in an agate mortar, transferred to the autoclave which was then filled with water up to a filling degree of 50%.After a reaction duration of oneweek, the autoclave was removed from the furnace and allowed to cool down to room temperature. The raw product was separated from themother liquor by vacuumfiltration,washedwithwater and acetone, and finally dried at 333 K. X-ray powder diffraction reveals that La2(HPO3)3 was not obtained as a single phased product.The sample containedLa(OH)3 and boric acid as crystalline impurities of which only the boric acid could be removed with an additional washing step. EDX analyses of isolated crystals comprise a ratioLa:P= 0.71which is in good agreement with the ratio of 2'3 obtained from the structure determination. Discussion Although rare earth phosphates(III) ((phosphites() have been investigated before [1-15], the crystal structure of La2(HPO3)3 has not been reported so far. Focusing on the lanthanoid compounds, the crystal structures of some hydrated compounds with the general composition Ln2(HPO3)3 · xH2O (Ln =Nd, Pr [8], Eu [9]; x = 1, 2.5) have been reported.Furthermore some acid lanthanum and neodymium phosphites with varying degree of protonation and water content are known: NdH(HPO3)2 [10], NdH(HPO3)2 ·H2O [11], La(H2PO3)3 ·H2O[12], La(H2PO3)(HPO3) · 3H2O[13], and LaH(HPO3)2 · 3H2O [14]. The crystal structure of Eu2(HPO3)3 [15] and Sc2(HPO3)3 [6] represent the only examples of rare earth phosphites with the same formula like the title compound.While the scandium phosphite comprises a structural arrangement of high symmetry due to the octahedral coordination of Sc ions [6], the europium compoundwith irregularly coordinated cations comprises structural similarities to the title compound but is not isotypic (monoclinic, space group C2/m). The crystal structure ofLa2(HPO3)3 contains two crystallographically independent distorted phosphite tetrahedra. These are considerably distorted due to differences inP—H (125(9) pm, 127(9) pm) and P—O (150.3(4) pm – 155.0(4) pm) distances and tetrahedral angles between 105(3)° and 118.4(3)° that clearly deviate from the ideal value.Size and shape of the phosphite groups are in good agreement with those found in related compounds. A view along the a axis (figure, top) shows that the complex anions are all pointing towards each other with the hydrogen corners. In this way hydrogen-lined channels parallel [100] are formedwhich are arranged layerwise along the b axis. Inbetween the phosphite channels corrugated layers of lanthanum cations are found.As the La cations are beaded along the [100] in a staggered fashion, surrounded exclusively by the oxygen atoms of the phosphite groups, this arrangement can as well be described by a channel motif.Both types of channels are shown as a cut out in the bottom figure. Three adjacent phosphite tetrahedra form the aperture (* ) 230 pm) of the hydrogen lined channels (A). Placed in oxygen lined channels (B), the crystallographically unique lanthanum is surrounded by seven phosphite groups and comprises irregular coordination by nine oxygen atoms. Z. Kristallogr. NCS 220 (2005) 533-534 533 © by OldenbourgWissenschaftsverlag, Munchen

Current-induced Conductance Jumps in Mechanically Controllable Junctions of La0.7Sr0.3MnO3 Manganites

The magnetic switching processes in mechanically controllable junctions (MCJ), made from high-quality single crystals of La0.7Sr0.3MnO3, are studied as a function of the DC current (up to 109 A/cm2) passing through the nanoconstriction. The current-voltage (I-V) curves of the MCJ are typical for an electron tunnelling process. By fitting I-V curves to the Simmons model, the barrier width (1 - 1.6) nm and height (0.4 - 1.7) eV of the junctions and their effective tunnel area (1-10) × 10−11 cm2 were estimated. Based on the close relation between transport properties and the magnetization in manganese compounds, we interpret the jumps in the conductance of MCJ, by integer multiples of e2/h, as due to the configuration reorientation of the magnetization of the Mn-ions clusters at the constriction surfaces.

Single-crystal growth of La2-2xSr1+2xMn2O7 under pressure

Large single crystals of La2−2xSr1+2xMn2O7 (x=0.3 to 0.525) have been prepared under controlled atmospheric conditions. The crystals were grown by the floating-zone technique in an image furnace under a mixed oxygen/argon atmosphere pressurized to 6–8×105 Pa. Rectangular single crystals with sizes up to 50×9×4 mm3 have been obtained. The phase-purity, composition, and quality of the crystals were analyzed by X-ray diffraction and electron probe microanalysis. The magnetic behavior is found to be sensitive to the composition of the atmosphere during growth.

Direct Production of Porous Cathode Material (La<SUB>1-<I>x</I></SUB>Sr<SUB><I>x</I></SUB>MnO<SUB>3</SUB>) Using a Reactive DC Thermal Plasma Spray System

The cathode material (La0.8Sr0.2MnO3) in solid oxide fuel cells (SOFCs) was plasma sprayed on mild steel in a reactive DC thermal plasma spray process. This high-speed process of depositing thin films for the components of SOFCs was examined experimentally. The results showed that a coating layer of La0.8Sr0.2MnO3 with a particular porosity could be obtained directly using both prereacted La0.8Sr0.2MnO3 and mixed raw materials (La2O3, SrCO3, and MnO or MnCO3) as feed materials with or without a pore former. The heat treatment of the plasma coating material at 1073 K (800 °C) for 3 h significantly enhanced the desired crystallization of La0.8Sr0.2MnO3 in the coated material.

The sound velocity, internal friction, and thermal expansion in a single crystal of La0.85Sr0.15MnO3

The results are given of the investigation of the temperature dependence of the sound velocity v, internal friction Q−1, and thermal expansion ΔL/L of a single crystal of La0.85Sr0.15MnO3 in the temperature range from 5 to 400 K. Clearly defined singularities of the elastic properties at a temperature of charge ordering Tco≈200 K are revealed. The results of X-ray diffraction studies performed at room temperature are used to determine the orientations and estimate the sizes of twins. The correlation between magnetic and structure inhomogeneities is established. Based on the results of analysis of the temperature dependence of internal friction and thermal expansion, an assumption is made of the presence in a single crystal of La0.85Sr0.15MnO3 of a structural transition in the temperature range from 15 to 60 K that has not been observed previously.

Magnetic resonance spectrum of a two-phase state in single crystals of La0.7Pb0.3MnO3 lanthanum manganite

Two absorption lines are observed over a wide temperature range below T c in the magnetic resonance spectrum of an La0.7Pb0.3MnO3 single crystal. These lines correspond to two magnetic phases in the sample. The frequency-field dependence of spectra obtained in the range of microwave radiation frequencies 10–77 GHz allows these phases to be interpreted as ferromagnetic and paramagnetic phases. The phase volume ratio depends on the temperature and the magnitude of the external magnetic field. Features in the temperature behavior of parameters of the magnetic absorption line are observed in the region of the highest magnetic resistance of the sample. The results are interpreted within the mechanism of electronic phase separation.

Cooperative nonradiative cross-relaxation in crystals of La(1−x)CexF3 solid solutions

The phenomenon of concentration quenching of the luminescence from donor ions in crystals of La1−x CexF3 solid solutions was studied. A cooperative nonradiative energy transfer from a single excited neodymium ion to a cooperative acceptor representing a couple of cerium ions, as well as from a single erbium ion to three cerium atoms (also forming a cooperative acceptor center), was observed.

Magnetic resonance in the layered manganite La1.2Sr1.8Mn2O7

We present electron spin resonance measurements on single crystals of La1.2Sr1.8Mn2O7. A well-resolved multiline spectrum is observed. There is one paramagnetic resonance line for temperatures above the ordering temperatures. The other lines turn out to arise from a small (< 0.1%) volume fraction of intergrowths.

Preparation and electric properties of La-doped-(Sr,Ba)TiO3 from sol-gel process

La-doped-(SrxBa1−x)TiO3 (La0.003(SrxBa1−x)0.997TiO3) powders were prepared by sol-gel process. The crystallization of La0.003(SrxBa1−x)0.997TiO3 was studied by means of XRD and DTA. The results showed that the perovskite phase was formed at 600 °C. The lattice parameters of the samples with different composition were measured at room temperature. The lattice constant and density decreased with increasing of x value in La0.003(SrxBa1−x)0.997TiO3. The La0.003(SrxBa1−x)0.997TiO3 sample achieved the lowest resistivity among all samples. The Curie temperatures (TC) of La0.003(SrxBa1−x)0.997TiO3 derived from dielectric constant – temperature curves decrease with increasing of x value. Voltage-current (V-I) property of the samples sintered at 1300 °C was measured by using HP4140B picoameter. Samples with lowest resistivity showed very good nonlinear V-I property. La0.003(SrxBa1−x)0.997TiO3 may be a potential candidate as varistor materials.

Anomalous behavior of the specific heat and upper critical magnetic field in the superconducting single crystal La1.85Sr0.15CuO4

The specific heat and resistive upper critical magnetic field of the single crystal La1.85Sr0.15CuO4 are investigated in the temperature range 2–50 K in magnetic fields up to 8 T for two directions of the magnetic field, parallel and normal to the ab crystalline plane. For both orientations a nonlinear (close to square root) magnetic field dependence of the mixed-state specific heat and a positive curvature of the temperature dependence of the upper critical magnetic field are observed. Neither of these anomalies is described by standard theories of superconductivity. Within the framework of the thermodynamic relations it is shown that in a type-II superconductor a relationship exists between the temperature dependence of the critical magnetic field and the field dependence of the specific heat. The anomalies observed in these phenomena are interrelated.