MgO Doping Research Articles

The effect of MgO doping on optical properties of LiNbO 3 single crystals

Undoped and MgO doped Lithium niobate single crystals were grown by the Czochralski technique. Comparative study of the optical properties of undoped and 7 mol% MgO doped LiNbO 3 crystal was undertaken. The effect of doping on refractive indices as well as second harmonic generation has been experimentally analyzed. The results of the polarization characteristics of second harmonic generation (SHG) support the major contribution of Li–O bonds to optical nonlinearity. MgO doping reduces the number of localized excitons and the grown LiNbO 3 crystal approaches the stoichiometric composition. This causes blue shift in the absorption edge of the crystals.

Application of periodically poled stoichiometric LiTaO3 for efficient optical parametric chirped pulse amplification at 1 kHz

We demonstrate optical parametric chirped pulse amplification (OPCPA) at 1-kHz repetition rate in periodically poled stoichiometric LiTaO3 (PPSLT) with 1 mol % MgO doping. Diode pumping was used both for the fiber laser generating the femtosecond seed pulses and the nanosecond laser/amplifier employed as a pump source. The high gain ( approximately 63 dB) and large bandwidth (20 nm) obtained for single-stage nondegenerate OPCPA operation provide a compact and efficient solution for amplification of ultrashort pulses near 1.57 microm. Stretched femtosecond pulses could be amplified up to 39.5 microJ in a 7-mm long, 2-mm thick sample of PPSLT. The pulse duration of the amplified signal pulses (FWHM) after recompression amounted to 315 fs.

Effect of Y 2O 3/MgO Co-doping on the electrical properties of base-metal-electroded BaTiO 3 materials

Effect of MgO and Y 2O 3 additions on modifying the dielectric constant-temperature (K–T curve) properties of the base-metal-electroded BaTiO 3 materials was systematically studied. The absolute value of (Δ C/ C) −55 °C and (Δ C/ C) 125 °C can be reduced, i.e., be moved upward, by incorporating large enough concentration of MgO and Y 2O 3 additives into the BaTiO 3, such that the K–T characteristics of the materials meet the X7R specification. The Y 2O 3 doping is more effective than the MgO doping in moving the (Δ C/ C) −55 °C and (Δ C/ C) 125 °C upward, which can be attributed to the fact that Y 2O 3 species addition flattens the K–T curves without shifting the Curie point of the materials. However, the proportion of Y 2O 3 incorporated into the materials should exceed the solubility of the BaTiO 3 materials such that the Y 2O 3 species can reside at the grain boundary region, forming a core-shell microstructure.

A study on periodic poling of different compositions of MgO:LiNbO3

LiNbO3 crystals doped with different amount of MgO have been produced using vapor transport equilibration technique. The poling characteristics of the crystals with different MgO doping levels have been investigated. The switching field and the spontaneous polarization Ps of the crystals were expressed as functions of crystal stoichiometry and Mg content. The switching field for the domain reversal in the near stoichiometric crystal with ［Li］/［Nb］=0.973 doped with 2.0mol.% MgO was 1.8kV/mm. This is about one twelfth of the switching field for the congruent crystal, and the pattern of the periodic domain in the crystal is better than in the congruent and stoichiometric crystal.

Polarization Switching of Pure and MgO-doped Lithium Niobate Crystals

We report here the polarization switching properties of pure and MgO-doped LiNbO3 crystals measured directly by applying an external electric field at room temperature. From hysteresis measurements, the ferroelectric intrinsic coercive fields are found to be decreased when the MgO concentration is increased. Spontaneous polarization is insensitive to the nonstoichiometric composition. The stability time of domain switching is strongly dependent on the MgO doping level. The strength of the internal field related to the non-stoichiometric defect will be discussed.

Effects of additives on the densification and microstructural evolution of fine θ-Al 2O 3 powder

The effects of MgO and NiO dopants on the densification and microstructural evolution of fine θ-Al 2O 3 powders have been investigated. The additives were added and mixed by solution coating and co-precipitation methods. The solubility diagrams of Al, Mg and Ni in aqueous solution were generated using computer programs DIASTAB for optimizing the mixing process. The results showed that small amount of both MgO and NiO dopants improve the densification and retard the grain growth of Al 2O 3 compacts during sintering. The average grain size of both Mg- and Ni-doped specimens are around 1.8 μm, and θ-Al 2O 3 transformed to α-Al 2O 3 completely during sintering at 1100 °C and higher temperatures.

Magnesia-doped HA/ β-TCP ceramics and evaluation of their biocompatibility

The sintering behavior, mechanical properties and biocompatibility of magnesia (MgO)-doped HA/TCP biphasic ceramics were studied. Pure HA/TCP ceramics showed poor sinterability due to the phase transformation of β- to α-TCP. MgO-doped HA/TCP ceramics showed high density without any phase transformation of β-TCP up to 1300°C, for MgO dopants incorporated into the β-TCP preferably and increased thermal stability of β-TCP. However, the addition of MgO higher than a critical content, suppressed grain growth of HA/TCP ceramics and lowered sinterability. The optimum amount of MgO doping was 1 wt%, which lead 99% relative density and higher mechanical properties than HA or β-TCP ceramics. From in vitro test and in vivo test, 1 wt% MgO-doped HA/TCP ceramics showed a good biocompatibility without cytotoxicity. After implantation under the muscle of rabbits, β-TCP phase was dissolved from the surface and a biological apatite covered the surface. These results proved that MgO addition increased drastically the sintering and mechanical properties of HA/ β-TCP ceramics without altering the biological safety and biocompatibility of the original composite.

Luminescence of pure and doped Al2O3 and MgO single crystals under inner-shell excitation

Luminescence properties of pure and doped MgO and Al2O3 single crystals were investigated under excitation by extreme ultraviolet radiation covering the L- and K-absorption edges of cations (Mg, Al) and anion (O), respectively. The excitation spectra of intrinsic and extrinsic emissions are antibate with respect to the absorption at the L-edges in both materials as well as at oxygen K-edge in Al2O3. Such behaviour is explained by non-radiative decay of electronic excitations at the surface. However, the efficiency of free exciton emission (7.6–7.7eV) shows a positive jump at the oxygen K-edge whereas the recombination impurity emission at 5.4eV has normal antibate behaviour with respect to the absorption in MgO. The origin of these effects is discussed.

Intrinsic and impurity luminescence and multiplication of excitations in complex oxides

The emission bands at 5.1 and 5.0eV have been detected at 9K in the cathodoluminescence spectra of pure and doped with Eu2+ ions BaMgAl10O17 and SrMgAl10O17 phosphors, respectively. A comparison of these emissions with the spectra of pure and doped MgO, α-Al2O3 and MgAl2O4 crystals allowed to interpret the VUV emissions of phosphors as the recombination of conduction electrons with the holes localized at oxygen ions near Mg2+ substituting Al3+ in spinel blocks. The creation regions of two or three electron–hole pairs by one photon of 22–32eV that causes the ionization of the 2p6 or 2s2 shells of oxygen in spinel blocks, has been separated in the excitation spectra of blue and UV emissions of BaMgAl10O17 at 9K. Besides thoroughly investigated 4f7→ 4f65d1 electron transitions in Eu2+ centres (absorption at 3.5–6.2eV), the creation region of the electronic excitations connected with the excitation and ionization of oxygen ions nearby Eu2+ or Mg2+ ions (6.6–7.8eV) can be tentatively separated in the excitation spectra of steady luminescence and recombination phosphorescence of SrMgAl10O17:Eu.

Doping of interfaces in (La0.7Sr0.3MnO3)1−x:(MgO)x composite films

Composite thin films of (La0.7Sr0.3MnO3)1−x:(MgO)x (x=0–0.5) were grown on Al2O3 (0001) substrates by a metalorganic aerosol deposition technique. A columnar growth of the films with the predominance of (111)- and (1̄10)-orientation was observed. Pure films (x=0) show a Curie temperature of TC=362 K, a metallic behavior accompanied with a low residual resistivity ρ∼10−4 Ω cm at T=4.2 K and a very small low-field magnetoresistance. Low amounts of MgO doping, x=0.05, result in a totally different electrical transport behavior which is a pronounced low-field magnetoresistance MR=25% at T=4.2 K. The MgO was found to be located at the interfaces between the grains thus building tunneling barriers and enhancing spin polarized tunneling similar to a system with vertical artificial tunnel junctions.

Hardness and elastic modulus from nanoindentations in nominally pure and doped MgO single crystals

Abstract Using a nanoindentation technique, the hardness and Young′s modulus were determined for nominally pure MgO single crystals and for MgO crystals doped with H, Li, Ni or Co impurities, subjected to different thermal treatments. The resulting defects were monitored by optical absorption spectroscopy. Undoped crystals have a hardness of 9.2 ± 0.2 GPa. After thermochemical reduction up to about 2300 K in Mg vapour at 7 atm, resulting in a deficiency of anions, a hardness value of 10.4±0.1 GPa was obtained. The enhancement is attributed to O vacancies. For doped crystals, hardening was observed and was attributed to impurities, point defects, cavities and metallic precipitates. A constant value of 300 GPa for Young′s modulus was obtained in all cases, indicating that the elastic properties are not influenced by either impurities or intrinsic defects.

Hardness and elastic modulus from nanoindentations in nominally pure and doped MgO single crystals

Hardness and elastic modulus from nanoindentations in nominally pure and doped MgO single crystals

Electrical and dielectric behavior of MgO doped Ba 0.7Sr0.3TiO 3 thin films on Al2 O3 substrate

In this letter, we present the results of the fabrication and characterization of 5 mol % MgO doped Ba0.7Sr0.3TiO3 (BST) films grown on Pt/TiN/SiO2 coated on Al2O3 substrates using the rf magnetron sputtering technique. The dielectric and electrical properties of Ba0.7Sr0.3TiO3 thin film were found to improve obviously by means of MgO doping. The leakage current density of BST thin film decreased about 1 order of magnitude on MgO doping, while BST film with MgO doping had a higher dielectric constant than that without MgO doping. The dielectric constant of the films increased with increasing annealing temperature due to the consistent increase in grain size and crystallinity. The 750 °C annealed, 100 nm thick film indicated a high dielectric constant of 440 at 100 kHz and the lattice constant of 3.986 Å. The improvement of the electrical properties of BST films was associated with the reduced oxygen vacancies due to improved oxygenation of BST films in the presence of MgO. The MgO doped BST films exhibited a high tunability of 25% and dc resistivity of 6×1010 Ω cm at an applied electric field of 200 kV/cm. The time-dependent dielectric breakdown studies indicated that the films had a longer lifetime of over 10 yrs on operation at the electric field of 0.4 MV/cm which is better than undoped BST film.

Near-Stoichiometric LiTaO 3 for Bulk Quasi-Phase-Matched Devices

Photorefractive damage at u =532 nm and green-light-induced infrared absorption (GRIIRA) of near-stoichiometric LiTaO 3 (SLT) single crystals were investigated. The SLT crystal even without MgO doping showed high photorefractive damage resistance and suppressed GRIIRA. In addition, a small amount of MgO doped into the SLT crystal almost eliminated the photorefractive damage and GRIIRA. A 3-mm-thick periodically poled SLT (PPSLT) and a 1-mm-thick periodically poled MgO-doped SLT (PPMgSLT) were successfully fabricated and their optical parametric oscillation (OPO) performances were investigated.

Nanoindentation on nominally pure and doped MgO crystals

Hardness and Young's modulus were determined in MgO crystals using a nanoindentation technique. Both nominally pure and hydrogen-doped crystals have a hardness of 9.1 GPa. After thermochemical reduction at 2200 K a hardness value of 10.2 GPa was obtained. Hardness enhancement is associated with oxygen vacancies induced by the thermal treatment. In lithium-doped crystals, the increase to 10.1 GPa after oxidation, and 9.9 GPa after reduction at 1873 K, was attributed to optically active defects absorbing at 1.8 eV and 5.3 eV, respectively. Doping with nickel increases the hardness to 10.1 GPa. Oxidation or reduction of MgO: Ni crystals do not further harden the crystals. In all these crystals, the Young's modulus was 290 GPa, indicating that the elastic properties are not influenced either by impurities or intrinsic defects.

Correlation between MgO Doping and Sintering Characteristics in Hydroxyapatite/β-Tricalcium Phosphate Composite

Correlation between MgO Doping and Sintering Characteristics in Hydroxyapatite/β-Tricalcium Phosphate Composite

Influence of MgO particle doping on flux pinning in Bi 2Sr 2CaCu 2O y crystals

Bi 2Sr 2CaCu 2O 8+ δ (Bi2212) single crystals embedded with MgO particles are successfully synthesized. The critical current density of Bi2212 single crystals with an appropriate amount of MgO doping is noticeably increased at low temperatures below 20 K with applied magnetic fields parallel to the c-axis as compared with undoped samples. Whereas at T⩾25 K, there is no extra flux pinning in MgO-doped samples. Microstructure analyses reveal that MgO doping induces a high density of dislocations in the ab plane of Bi2212 matrix, which may be responsible for the enhanced flux pinning at low temperatures.

Gas-phase hydrogenation of adiponitrile with high selectivity to primary amine over supported Ni-B amorphous catalysts

Gas-phase hydrogenation of adiponitrile (ADN) was performed at 1 atm pressure over the Ni-B/SiO 2 amorphous catalyst, which exhibited high selectivity to 1,6-hexanediamine (HDA) at 100% ADN conversion. The selectivity to HDA could be further enhanced by MgO dopant. The product analysis revealed that the selectivity to HDA was mainly dependent on the contents of 6-aminohexanenitrile and azacycloheptane formed during the ADN hydrogenation. The 6-aminohexanenitrile was an intermediate in the reaction; it resulted from the half-hydrogenation of ADN; and its content was strongly affected by the activity of the catalyst. The azacycloheptane was a side-product (secondary amine) formed via the nucleophilic addition of the primary amine on one side of ADN chain to the aldimino carbon atom on the other side which was adsorbed by the Ni active sites. The electronic density of the Ni active sites played a key role in determining the content of azacycloheptane. The presence of the alloying B resulted in the electron-enriched Ni active sites which effectively inhibited the formation of azacycloheptane and in turn, resulted in the high selectivity to HDA.

Determination of genuine diffusivities in heterogeneous media using stimulated echo pulsed field gradient NMR.

Pulsed field gradient (PFG) NMR diffusion measurements in heterogeneous media may lead to erroneous results due to the disturbing influence of internal magnetic field gradients. Here, we present a simple theoretical model which allows one to interpret data obtained by stimulated spin echo PFG NMR in the presence of spatially varying internal field gradients. Using the results of this theory, the genuine self-diffusion coefficients in heterogeneous media may be extrapolated from the dependence of the apparent diffusivities on the dephasing time of the simulated echo PFG NMR sequence. Experimental evidence that such extrapolation yields satisfactory results for self-diffusion of hexadecane in natural sediments (sand) and of n-octanol in doped MgO pastes is provided.

Pb substitution effects on the critical current density in MgO doped Bi2212 crystals

For heavily Pb substituted Bi2212 crystals with MgO doping, we found not only the critical current density J/sub c/ anisotropy decreasing to a half as much as Pb free MgO doped crystals but J/sub c/ and irreversibility field B/sub irr/ improvement. Apparent pinning potential U/sub 0/* derived from flux creep experiments for these crystals also increased. Those results suggest that the effect of MgO doping is more pronounced by decreasing the J/sub c/ anisotropy of crystals. Dislocation increase in the Pb substituted Bi2212 crystals due to MgO doping was observed with a transmission electron microscope.