Cu-doped Crystals Research Articles

Effect of Cu Doping on Structure and Physical Properties in the Antiferromagnetic Dirac Semimetal CaMnBi2.

The newly discovered AMnBi2 (A = Ca, Sr, Ba, Eu, and Yb) materials composed of two-dimensional Bi square nets provide an excellent platform to investigate the effect of magnetism on topological band structures. Effectively tuning the magnetic interaction in AMnBi2 is of great importance to advance this issue. Here, we describe an effective route to tune the magnetism in Dirac semimetal CaMnBi2 through Cu doping. Structural analysis on CaMn1-xCuxBi2 single crystals indicates that Cu atoms occupy the Mn sites randomly, with the maximum doping level of 25%. After Cu doping, the Bi square net in charge of the Dirac band is still retained, but the Bi-Bi bond distance is markedly shortened. The antiferromagnetic interaction of CaMnBi2 is strongly weakened in the Cu-doped crystals, with the transition temperature decreased from 260 to 85 K. On the contrary, the ferromagnetic component that originated from the canted AFM is enhanced, suggesting that the spin canting in this system is tunable. In addition, the magnetoresistance is decreased upon Cu doping, probably due to the disorder in structure. Our work suggests that the CaMn1-xCuxBi2 (0 ≤ x ≤ 0.25) system can offer a suitable playground to address the interplay between magnetism and the topological state.

Luminescence properties of the Pb2MoO5 single crystals doped with Cu ions

Photoluminescence (PL) emission and PL excitation spectra of the undoped and Cu- doped Pb2MoO5 grown by Czochralski technique are obtained and analyzed. The complex wide PL emission band in 450-750 nm spectral range was observed for both pure and Cu- containing crystals under photoexcitation with ultraviolet light. The short-wavelength component of the PL has been associated with luminescence centers related to MoO42− anionic groups. Long-wavelength the PL component with maxima near 600 nm was observed for both pure and Cu-doped crystals and it is described to manifestation of the crystal defects.

Quasi-periodic magnetic flux jumps in the superconducting state of Ba0.5K0.5Fe1.9M0.1As2 (M = Fe, Co, Ni, Cu, and Zn)

Polycrystals of Ba0.5K0.5Fe1.9M0.1As2 (M=Fe, Co, Ni, Cu, and Zn) synthesized at high pressures show quasi-periodic spikes in the magnetization loop at 2K owing to successive flux jumps, while the single crystals are observed as absence of jumps. The Zn-doped crystal indicates higher frequency flux jumps than that of Zn-free samples, because of the reduction of grain size and enhancement of grain boundary effect. However, the Co-, Ni- and Cu-doped crystals show less jumps duo to the increased granularity. Our present results suggest that the flux jump in the textured polycrystals is controlled largely by the grain boundary as the flux pining effect rather than the intrinsic dopants.

Photorefractive properties of lithium niobate single crystals doped with copper

Raman scattering with excitation in the ultraviolet, visible, and near infrared and electron paramagnetic resonance are used to study the photorefractive properties of nominally pure, stoichiometric (R = Li/Nb = 1) single crystals of lithium niobate grown from a melt with 58.6 mol% Li2O (LiNbO3stoich), nominally pure crystals with a congruent composition (LiNbO3congr, R = 0.946), and Cu-doped crystals with a congruent composition (LiNbO3:Cu, [Cu] = 0.015 mass%). Optical irradiation is found to cause charge exchange of copper cations, Ca2+ → Cu, in the LiNbO3:Cu ([Cu] = 0.015 mass%) crystals. Thus, crystalline LiNbO3:Cu ([Cu] = 0.015 mass%) manifests photorefractive properties as a result of charge exchange of copper ions during laser irradiation, in addition to the contribution from intrinsic defects with localized electrons previously observed in LiNbO3stoich and LiNbO3congr.

Light-induced charge-transport in undoped LiNbO3 crystals

Light-induced charge transport in nominally undoped LiNbO3 crystals essentially differs from that in Fe- and Cu-doped crystals. Furthermore, it is of relevance for numerous effects ranging from optical damage to domain reversal. Here, we review the state of the art of the studies of light-induced charge transport in this important material. This includes a summary of the facts known for doped crystals, a description of the experimental methods relevant to undoped crystals, a summary of the main experimental data for this material, especially the data on the intensity dependences, presentation of the methods of purification from unwanted photo-active electrons, and a discussion of possible mechanisms responsible for the charge-transport peculiarities.

Electron configuration and charge state of electrically active Cu, Ag and Au ions inZnSe

The Hall effect, electrical conductivity and electron mobility are investigated attemperatures between 55 and 500 K in n-ZnSe crystals doped with Cu, Ag or Au. Thepresence of a small amount of Cu atoms leads to an inversion of the sign of the Hallcoefficient at temperatures above 300 K. Anomalous temperature dependenceof the electron mobility is observed in the samples with low Cu concentration(<0.3 at.% in the melt). Different characters of the temperature dependences of kineticcoefficients are found for n-ZnSe doped with Ag and Au. These curves are typical forcrystals having several donor levels at different energetic depths. Immediately afterdoping, silver behaves like a usual compensating acceptor impurity while gold showsamphoteric properties. We propose a model that explains the anomalies of thetemperature dependences of the kinetic coefficients in Cu-doped crystals and thelack of the anomalies in Ag-doped and Au-doped crystals. In accordance withthis model and our experimental data, copper in n-ZnSe has two charge states,CuZn+ (d10)and CuZn2+ (d9), and two acceptor levels near the valence band. Silver and gold exist in single-charged statesAgZn+ and AuZn+ with d10 electron configuration forming single energy levels near the valence band. Au atoms form mainly interstitialAui donors at low doping concentrations and substitutionalAuZn and AuZn-based acceptors at high doping concentrations. Time stimulation of the amphotericproperties of Ag is discussed.

High temperature electrical conductivity in the phase transition region

ZnS and CdSe x Te 1− x solid solutions were investigated by the method of high temperature electrical conductivity (HTEC) as a function of sample temperature and component vapour pressure in the phase transition region. On the temperature dependence of conductivity, a sharp jump of conductivity was observed in this region. On the temperature raising branch of the HTEC isobar the step-like change occurred at a higher temperature than on the temperature lowering branch. In the case of ZnS, the conductivity jump is dependent on p Zn in undoped and Cu-doped crystals and independent of p Zn in Al- and Ga-doped crystals. The X-ray diffraction investigations in CdSe x Te 1− x solid solutions show the simultaneous existence of cubic and hexagonal phases between the temperatures of step-like changes of HTEC.

Photoemission of Ag, Cu, and Ge-doped α-Ga 2S 3 crystals

Photoluminescence of α-Ga 2S 3 crystals doped with the Ib elements (Ag, Cu) and the IVb element (Ge) has been observed. The dominant emission band corresponding to the 2.38 eV green-band in the undoped crystals appears at 2.50 eV in the Ag-doped crystals and 2.41 eV in the Cu-doped crystals. In the Ge-doped crystals, the dominant emission band is situated at 2.10 eV. Applying the Prener-Williams model, it is concluded that the Ib element (Ag or Cu) in Ga 2S 3, like the Ga-vacancy, can be an activator having the nature of acceptor and causes the donor-acceptor pair emission associated with an iodine shallow donor of coactivator which is imbeded for the iodine-transport crystal growth. On the other hand, Ge can be considered to be a donor at 0.28 eV below the conduction band. Additional measurements of thermoluminescence, infrared absorption and optical absorption near the band gap support the above conclusion.

Photoluminescence properties of Cu-doped GaSe

Photoluminescence spectra of undoped and Cu-doped crystals of the layered semiconductor GaSe have been measured in the temperature range from 80K to room temperature. The main modification of the spectra in doped crystals with respect to those of undoped samples is the appearance of two new bands and the enhancement of light emission. A detailed analysis of spectra, by varying excitation intensity and temperature, enabled the authors to analyse the defect levels involved in the transitions. A simple kinetic model for indirect free and bound excitonic transitions in doped samples is proposed.

Behavior of Copper Impurity in ZnSe

The luminescence and diffusion behavior of copper impurity in ZnSe has been studied by the substoichiometric isotope dilution analysis and photoluminescence measurements. The copper-green emission is prominent in higher Cu-doped crystals, while the copper-red emission is prominent in lower copper concentration ZnSe. Copper acts as the killer center against the near-band edge blue emission. The characteristics of the recombination centers have been examined for temperature dependence of the emission peak energy and emission intensity as well as excitation spectra. It is clear from the photoluminescence and the substoichiometric isotope dilution analysis that the copper impurity can be removed from ZnSe crystals by Zn heat treatment. The measurements show that the diffusion coefficient of Cu in the undoped and Cu-doped ZnSe in the temperature range above 500°C obeys the relationship D=1.26×10-2exp (-1.0 eV/kT).

Pure and doped barium titanate. Crystal growth and chemical composition

Barium titanate single crystals are grwon in two ways, i.e. by the Remeika and the Czochralski method. Doping ions (FeCoCu) are introduced into Remeika crystals and determined by a spectro photometric method. Impurity ions (FKPtSb) are determined in both kinds of crystals; pulled crystals are purer than Remeika crystals. The stoichiometry Ti/Ba + Sr is excellent in pulled crystals but the Ti, Ba, Sr, K concentrations in Cu-doped crystals show ion size effects in the compensation mechanism.

ChemInform Abstract: A MACROCYCLIC TETRADENTATE COMPLEX STRUCTURE OF 1,4,8,11‐TETRATHIACYCLOTETRADECANENICKEL(II) TETRAFLUOROBORATE, NI(TTO)(BF4)2, AND ELECTRON PARAMAGNETIC RESONANCE SPECTRA OF ITS (63)CU‐DOPED CRYSTALS

Chemischer InformationsdienstVolume 6, Issue 42 Organoelement Compounds ChemInform Abstract: A MACROCYCLIC TETRADENTATE COMPLEX STRUCTURE OF 1,4,8,11-TETRATHIACYCLOTETRADECANENICKEL(II) TETRAFLUOROBORATE, NI(TTO)(BF4)2, AND ELECTRON PARAMAGNETIC RESONANCE SPECTRA OF ITS (63)CU-DOPED CRYSTALS P. H. DAVIS, P. H. DAVISSearch for more papers by this authorL. K. WHITE, L. K. WHITESearch for more papers by this authorR. L. BELFORD, R. L. BELFORDSearch for more papers by this author P. H. DAVIS, P. H. DAVISSearch for more papers by this authorL. K. WHITE, L. K. WHITESearch for more papers by this authorR. L. BELFORD, R. L. BELFORDSearch for more papers by this author First published: October 21, 1975 https://doi.org/10.1002/chin.197542407AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue42October 21, 1975 RelatedInformation