C-axis Lattice Constant Research Articles

Similarity of crystalline structure of BSCCO single crystal and multi-layer film

Bi 2Sr 2CaCu 2O y single crystal was studied by means of high-resolution X-ray diffraction and the local work function measurement with scanning tunneling microscope (STM). The results show that the single crystal is natively inhomogeneous. The rocking curve of 0 0 l reflection indicates that the c-axis lattice constant of the crystal varies in a narrow range, clearly showing a multi-layer character. The reflectivity measurement supports this result. It shows an obvious multi-layer character too. The small angle scattering indicates that although the c-axis lattice constant is little different in the crystal, it shows a long period of about 340 Å. The local work function measurement with STM demonstrates that the crystal is inhomogeneous. Some part in the crystal acts like thin film and some part like substrate, supporting the results of X-ray analyses.

Growth of La-doped Bi 2Sr 2CaCu 2O y single crystals by a self-flux method

We prepared La-doped Bi 2Sr 2CaCu 2O y (Bi(La)-2212) single crystals by a self-flux method and investigated the effects of La concentrations on their superconducting properties. The plate-like single crystal with a size of 6×8 mm 2 was obtained by using the starting material of Bi:Sr:La:Ca:Cu=2:1.9:0.1:1:2. In addition, the single crystals tended to be large with increasing the temperatures for melting. From the results of X-ray diffraction (XRD) patterns, we found that the La-doped single crystals were Bi-2212 single phase and that the c-axis lattice constant of the single crystals became short with increasing La concentration x in the starting materials of Bi 2Sr 2− x La x CaCu 2O y .

Superconducting properties ofCu1-xTlxBa2Ca3Cu4O12-y thinfilms

Superconducting thin films with a predominant single phase ofCu1-xTlxBa2Ca3Cu4O12-y [Cu1-xTlx-1234] have beenprepared for the first time by employing a two-step method. In this method thecrystalline material was prepared from the sputtered amorphous phase bythallium treatment. This process was carried out at 900 °C for 1 h inan Au capsule. The amorphous phase was prepared by sputter deposition onto anSrTiO3 substrate from a stoichiometric target of compositionCuBa2Ca3Cu4Ox. The films achieved after thallium treatment werealigned bi-axially along the a- and c-axes. XRD (x-ray diffraction)measurements showed a single-phase material with a c-axis lattice constantof 18.74 Å. The c-axis lattice constant of Cu1-xTlx-1234 films isin between that of Cu-1234 (17.99 Å) and Tl-1234 (19.11 Å)superconductors. The pole figure measurements of 103 reflection of the filmsshowed a-axis-oriented crystals with Δϕ = 0.8°. The compositionof the films after EDX (energy dispersive x-ray spectroscopy) measurements wasCu0.3Tl0.7Ba2Ca3Cu4O12-y. From the resistivitymeasurements Tc was 110 K and Jc measurements showed a current densityof 2.0×106 A cm-2 (77 K, 0 T). The preparation ofCu1-xTlx-1234 superconductor films by this method was highlyreproducible.

Influence of [K]/[Li] and [Li]/[Nb] ratios in melts on the TSSG growth and SHG characteristics of potassium lithium niobate crystals

KLN crystals were grown along the 〈110〉 axis by the TSSG method from different melts with 30–32mol% K2O, 23–27mol% Li2O and 43–46mol% Nb2O5. Lattice constants were measured by the single crystal XRD analysis. Curie temperatures were determined with an LCR meter HP 4284A at 1kHz. The blue SHG characteristics of the KLN crystals were investigated by using a 3900S Ti: sapphire CW tunable laser with the wavelength range of 675–1100nm. It is found that the non-critical phase matching (NCPM) wavelength at room temperature decreases significantly from 974 to 827.4nm with the increase of [K]/[Li] and [Li]/[Nb] ratios in the melts. On the basis of this survey, the melt compositions suitable for the TSSG growth of high quality KLN crystals with high lithium content are outlined, as indicated by the large c-axis lattice constant, high Curie temperature and short NCPM wavelength.

Composition-dependent layered structure and transport properties in BiTe thin films

We have studied the compositional dependence of the layered structure of ${\mathrm{Bi}}_{1+x}{\mathrm{Te}}_{1\ensuremath{-}x}$ thin films and its relation with the transport properties. We have observed that the ${\mathrm{Bi}}_{1+x}{\mathrm{Te}}_{1\ensuremath{-}x}$ films have a stable structure near the ${\mathrm{Bi}}_{1}{\mathrm{Te}}_{1}$ composition and that their crystallinity depends strongly upon the compositional deviation from stoichiometric ${\mathrm{Bi}}_{1}{\mathrm{Te}}_{1}.$ We have determined possible layered structures, configured with two sequences of Bi--Bi and Te--Bi--Te--Bi--Te, corresponding to Bi and Te binary compositions using x-ray diffraction analysis. Their c-axis lattice constants were in the range of 36 \AA{} and 136 \AA{}. Temperature-dependent thermopowers of the films reveal that as the composition changes from Te rich to Bi rich, the polarity varies from n type to p type.

Pulsed Laser Deposition and Characterization of Zn1−xMnxO Films

AbstractHere we present our results of structural, optical, and magnetic measurements of Zn1−xMnxO thin films. These films were grown epitaxially on (0001) sapphire substrates by using pulsed laser deposition technique. The maximum Mn content (x=0.36) is found to be much higher than allowed by thermal equlibrium limit (x∼0.13) due to the non-equilibrium nature of the pulsed laser deposition. All the films investigated here were found to be single phase with <0001> orientation epitaxial relationship. A linear increase in the c-axis lattice constant was observed with increase in Mn concentration. Optical transmittance measurements showed an increase in the insulating band-gap (Eg) with increase in Mn concentration. DC magnetization measurements showed that there is no long range ferromagnetic ordering down to 10 K.

The lattice relaxation of ZnO single crystal (0001) surface

Wurtzite-type ZnO is a polar crystal whose (0001) surface is terminated by Zn ions. The ZnO single crystals were etched for the surfaces to have regular step/terrace structures and analyzed by reflection high-energy electron diffraction (RHEED) and coaxial impact-collision ion scattering spectroscopy (CAICISS). RHEED patterns showed that the surface had a 1×1 structure. From the polar angle dependence of CAICISS time-of-flight spectra for Zn ions, a peak due to a focusing effect for fifth-layer Zn ions by the first-layer Zn ions was observed at 49.5°, which was 2° higher than the corresponding angle simulated for a non-relaxed surface. These results indicated that the uppermost Zn ions were surface-normally relaxed toward the outside of the surface by about 7% of the c-axis lattice constant.

Structure and magnetic properties of barium hexaferrite films deposited at low oxygen pressures

Barium hexaferrite films were grown by pulsed laser ablation deposition onto c-plane sapphire at oxygen pressures from 1 to 200mTorr to evaluate their structural and magnetic properties. Films deposited at pressures above 1mTorr showed excellent c-axis orientation normal to the film plane, and good surface morphologies. The c-axis lattice constant of films deposited at and above 50mTorr was reduced compared to bulk values. Film saturation magnetization values were slightly lower than bulk values, while anisotropy field values were comparable. Ferrimagnetic resonance measurements showed distinct absorption peaks, with the narrowest linewidth of 0.20kOe being measured for a 10mTorr film. The 1mTorr film had a significantly different texture wherein the c-axis laid down into the film plane, and also showed in-plane six-fold magnetic anisotropy. These results may indicate that highly c-axis oriented barium hexaferrite films can be grown to greater thicknesses using reduced oxygen pressures.

Cracking and Delamination of Heteroepitaxial Barium Hexaferrite Films

ABSTRACTExperimental results are shown for the structural and stress behaviors of c-axis oriented barium hexaferrite films on c-plane sapphire (Al2O3) substrates as a function of oxygen growth pressure and film thickness. It is shown that films deposited at 20 mTorr crack and delaminate at thicknesses above 15 µm, but that evidence for these large stresses is not apparent in either substrate curvature measurements or distortion of the c-axis lattice constant for thinner films (< 2 µm). In contrast, films (< 4 µm) deposited at 300 mTorr show large substrate curvatures that relax with increasing film thickness, in tandem with the formation of first large outgrowths, and then polycrystalline grains as the original c-axis film texture is randomized. Correlations between these observations are made to explain the complex evolution of properties in these films.

Preparation of biaxially oriented TlCu-1234 thin films

The single phase of TlCu-1234 superconductor thin films is prepared for the first time by the amorphous phase epitaxy (APE) method, which is thallium treatment of sputtered amorphous phase at 900°C for 1 h. The amorphous phase is prepared by sputtering from the stoichiometric target composition CuBa 2Ca 3Cu 4O 12− y . The films on the SrTiO 3 substrate are aligned biaxially after the thallium treatment. Highly reproducible TlCu-1234 films are prepared by this method. The XRD reflected a predominant single phase with the c-axis lattice constant of 18.74 Å. This lattice constant value is in between that of Cu-1234 (17.99 Å) and Tl-1234 (19.11 Å). The pole figure measurements of (103) reflection of the films showed a-axis-oriented crystals with Δ φ=0.8°. The composition of the films after Energy Dispersive X-ray (EDX) measurements is Tl 0.8Cu 0.2Ba 2Ca 3Cu 4O 12− y . From the resistivity measurements, the T c is 113 K. Preliminary J c measurements showed a current density of 1.0×10 6 A/cm 2 (77 K, 0 T).

Thickness dependence of structural and electrical properties in epitaxial lead zirconate titanate films

We have studied the effect of misfit strain on the microstructure and properties of ferroelectric lead zirconate titanate thin films. We have changed the misfit strain by varying the film thickness and studied the thickness effect on the domain formation of epitaxial PbZr0.2Ti0.8O3 (PZT) films grown by pulsed laser deposition on (001) LaAlO3 substrates with La0.5Sr0.5CoO3 (LSCO) electrodes. The nominal thickness of the PZT films was varied from 60 to 400 nm with the LSCO electrode thickness kept constant at 50 nm. X-ray diffraction experiments show that the films relax via the formation of a domains, the fraction of which increase with the ferroelectric film thickness. The c-axis lattice constant of PZT films calculated from the 002 reflection decreases with increasing film thickness and approaches the bulk value of ∼0.413 nm in the films thicker than 300 nm. Cross-sectional transmission electron microscopy images reveal that the a-domain fraction and period increase with increasing film thickness. The relaxation of misfit strain in the film is accompanied by systematic changes in the polarization properties, as well as the switching fields, quantified by the coercive field and the activation field.

Properties of pulsed laser deposited scandium-doped barium hexaferrite films

The properties of thin films of BaScxFe12−xO19 (x=0.4) were determined by structural and magnetic measurements. Films were deposited by pulsed laser ablation deposition onto c-plane sapphire at oxygen pressures between 10 and 100 mTorr. X-ray diffraction measurements showed all films to be single-phase c-axis oriented hexaferrites with expanded c-axis lattice constants compared to x=0 films. Magnetometry measurements showed that all films had the easy axis (c-axis) normal to the film plane, with a mean saturation magnetization value of 3.8 kG. The mean uniaxial anisotropy field value was 10.6 kOe. This ability to adjust the uniaxial anisotropy field in hexaferrite films through selective substitution will be important for future planar microwave devices.

Preparation and properties of c-axis-oriented NdBa 2Cu 3O 7− δ films by dc sputtering

NdBa 2Cu 3O 7− δ (NdBCO) is known to have the highest T c, among the rare earth REBa 2Cu 3O 7− δ (RBCO) family, and to show higher irreversibility fields than YBa 2Cu 3O 7− δ (YBCO). Recently, excellent superconducting NdBCO films have been synthesized by a laser ablation technique. In this work, the transition temperature, phase and growth morphology of NdBCO films deposited on (100) SrTiO 3 (STO) and (100) MgO substrates by dc sputtering have been investigated. The transition temperature T c is closely related with the c-axis lattice constant and shows a maximum around 1.173 nm. The c-axis lattice constant of the films strongly depends on oxygen pressure P o. High- T c NdBCO films are obtained around P o=350 Pa. The spiral growth morphology of the films is affected by deposition rate and takes place at low deposition rate. The best film has shown a zero resistance transition temperature of 92.6 K.

Epitaxial growth of Pb(Zr, Ti)O3/(La, Sr)CuO4 heterostructureson SrTiO3 by magnetron sputtering

Pb(Zr0.53Ti0.47)O3/(La2-xSrx)CuO4 (PZT/LSCO) heterostructures have been prepared by magnetron sputtering. X-ray diffraction showed that both c-axis oriented PZT and LSCO layers epitaxially grow on (100) SrTiO3 and the c-axis lattice constant of the LSCO film increases with the growth of the PZT film. It was found from atomic force microscopy observations that the typical grain size is in the range 200~250 nm for a PZT layer with a thickness of 200 nm; the root mean square roughness of the surface of PZT layer is ~30 Å. Transmission electron microscopy observation shows that an ~3 nm thick interface layer exists between PZT and LSCO. The capacitance measurement for the configuration of Ag/PZT/LSCO showed that the dielectric constant of this kind of heterostructure quite strongly depends on temperature and frequency.

Influence of Re substitution on the flux pinning in (Hg,Re)Ba 2Ca 2Cu 3O 8+ δ single crystals

Flux pinning in Hg 0.77Re 0.23Ba 2Ca 2Cu 3O 8+ δ single crystals ( T c=130 K) and in HgBa 2Ca 2Cu 3O 8+ δ crystals with T c equal to 130 and 120 K was studied. In the investigated crystals Re atoms substitute at the Hg site of HgBa 2Ca 2Cu 3O 8+ δ and alter the defect structure of the host layer by pulling in four new oxygen atoms at (0.34, 0.34, 0) position to form an octahedron around Re. As a result a significant improvement of the irreversibility line position at the H–T phase diagram for Hg 0.77Re 0.23Ba 2Ca 2Cu 3O 8+ δ crystal is observed only at low temperatures (below 80 K). However, magnetization measurements performed at temperatures above 100 K show insignificant change in the irreversibility line position only, as compared to that one of the parent compound with T c=130 K. This indicates insignificant influence of new pinning centers, introduced by Re substitution, in the temperature range, where thermal activation energy becomes significant in comparison with pinning energy. Furthermore, obtained data indicate that no improvement of the coupling between superconducting layers was achieved as a result of the expected increase of electrical conductivity in the blocking layer. Since only a small change in the c-axis lattice constant was observed in Re substituted crystals, we can conclude that a larger shortening of the blocking layer in the material is necessary to improve the irreversibility line position in HgBa 2Ca 2Cu 3O 8+ δ crystals at high temperatures.

Effect of Grain Size on Bi4Ti3O12 Thin Film Properties

Bismuth titanate (Bi4Ti3O12) thin films with a c-axis orientation were prepared on (100) silicon wafers by rf magnetron sputtering. The average grain size and the c-axis lattice constant depend on the substrate temperature. The c-axis lattice constant was decreased with increasing grain size. The leakage current characteristics of the Bi4Ti3O12 thin film consisting of small grains with a closely packed structure, are superior to those of others. The apparent remanent polarization and the apparent coercive field of the film with small grain sizes were estimated to be 2.4 µC·cm-2 and 2.3 kV·cm-1, respectively. The refractive index dispersion characteristics for the film show that the large grains increase the distortion of the oxygen-octahedra. Consequently, this result indicates that the small grain size of Bi4Ti3O12 thin films can improve the ferroelectric properties.

SuperconductingPrBa2Cu3Ox

${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ grown by the traveling-solvent floating-zone method shows a large inhomogeneity both in structural and physical properties, such as lattice parameters and transport and magnetic properties. Some parts of this sample exhibit bulk superconductivity. The c-axis lattice constant is longer than that of nonsuperconducting samples grown by the flux method. However, the magnetic susceptibility of the superconducting sample suggests the valence of Pr is $+3$. The superconducting transition temperature exceeds 100 K under a pressure over 8 GPa and still has a potential to increase.

Sol-gel-derived c-axis oriented ZnO thin films

c-Axis oriented zinc oxide thin films were prepared by sol-gel process on fused quartz substrates. The structure, optical and electrical properties of ZnO films were investigated. Growth of the thin films strongly depends on heat-treatment conditions. The c-axis lattice constants of the thin films and the band gap are a little bigger than that of ZnO crystal. The differences between the thin film and crystal might be attributable to the grain boundaries and imperfections in thin films.

Study of structures and dielectric dispersion behavior of BaTiO 3/YBa 2Cu 3O 7−x bilayer films

The structures of BaTiO 3/YBa 2Cu 3O 7−x bilayer films and their low frequency dielectric dispersion behavior were investigated. With the increase of BaTiO 3 film thickness, the crystallinity of the BaTiO 3 films gets better and the c-axis lattice constants become smaller. It is shown that the ion-vacancy migration, related to film structures, film defects and boundaries, plays an important role in the low frequency dielectric dispersion behavior.

Process optimization for the fabrication of Tl2Ba2Ca2Cu3O10 thin films

A process has been developed for the fabrication of nearly single phase superconducting Tl2Ba2Ca2Cu3O10 thin films on (100) LaAlO3 substrates with a superconducting transition temperature Tc of 120 K and low microwave surface resistance at temperatures up to 110 K. Amorphous BaCaCuO precursor films were first deposited by rf magnetron sputtering and then thallinated at elevated temperatures. The double TlO layer phases (Tl2Ba2Ca2Cu3O10 + Tl2Ba2CaCu2O8) formed preferentially over the single TlO layer phases (TlBa2Ca2Cu3O9 + TlBa2CaCu2O7) at high Tl2O partial pressures. Thin films containing Tl2Ba2Ca2Cu3O10 and a small amount of CuO were prepared from Cu-rich precursor films (Cu/Ba > 1.7), while lower Cu content led to the formation of Tl2Ba2CaCu2O8 as a secondary phase. Tl2Ba2Ca2Cu3O10 film epitaxy was enhanced by carrying out the thallination in reduced oxygen partial pressures of 0.01–0.05 atm. Following the thallination step, the Tl2Ba2Ca2Cu3O10 thin films had a superconducting transition temperature Tc of only 106 ± 4 K. An additional 62 h anneal at 800 °C or an 8 h anneal at 850 °C in a Tl2O/O2 atmosphere increased the Tc to 120 K. The increase in Tc was accompanied by a decrease in the c-axis lattice constant, an enhancement in the long-range order in the c-direction, and the formation of a small amount of Tl2Ba2CaCu2O8 as a secondary phase. Minimization of surface resistance at high temperature (95–110 K) requires that the fraction of Tl2Ba2CaCu2O8 secondary phase in the films be kept low. Process routes are also described for the formation of nearly single phase TlBa2Ca2Cu3O9 and TlBa2CaCu2O7 thin films and the formation of a new ordered intergrowth phase, Tl4Ba4Ca3Cu5O18, which consists of alternating Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 layers.