Search

In general, it is hard to grow large single crystals with a one-dimensional chain structure due to the preferred growth direction and chain breakage. Most reported one-dimensional lead iodine chain single crystals can grow long, but they are difficult to grow thick. Here, we demonstrate for the first time the growth of 2 mm × 4 mm × 8 mm sized single crystal one dimensional organic lead iodine perovskite – DMAPbI3 ((CH3)2NH2PbI3). Benzylamine addition to the solution may help to dissolve crystals with high defect concentrations so that the crystal can grow larger. Through the measurement on the large single crystal, we found that DMAPbI3 is ferroelectric below 260 K, and the dielectric constant of DMAPbI3 at various frequencies at room temperature is as high as more than 100. Blue photoluminescence centered at 2.6 eV was reported. The ferroelectricity of DMAPbI3 may be used to design more stable and efficient organometal halide perovskite solar cells and photoelectric devices. [ABSTRACT FROM AUTHOR]

Perfect and defective surface structures for (001) SrTiO3 are determined in considering a supercell with 11 atomic layers using the first-principles calculations. The amplitude of the surface rumpling for the SrO-terminated surface is much larger than that for the TiO2-terminated surface, although both SrO- and TiO2-terminated surfaces are stable for a comparable range of the TiO2 chemical potential. The distance between the first and second planes compresses while that of the second and third planes expands due to the relaxation of the slab. The top sites of the oxygen atoms of SrO-termined surface and the fourfold symmetry hollow sites of TiO2-termined surface are favorable for Ti or Sr adsorbate. The relative stability of the defect species or reactions varies with the equilibrium conditions. The dominant surface defect is Ti substitutional defect and a TiO–TiO2 double layers may form at the surface, which has been confirmed by experiments. [ABSTRACT FROM AUTHOR]

Structural and magnetocaloric properties for the perovskite manganite La2/3-xYxCa1/3-ySryMnO3 (x<0.2) have been studied. These compounds with the fixed A-site average ionic radii of 1.204 Å and Mn4+/Mn3+ ratio were prepared by conventional solid-state reaction technique. The lattice parameters were obtained from refining x-ray diffraction diagrams preformed by Rietveld refinement method. The ferromagnetic ordering temperature TC increases abruptly owing to the increase in the competition between A-site size-disorder degree σ2 and double-exchange interaction resulting from Mn–O–Mn bond angle. Phase transition may be broadened due to the cation disordering at A-site. Sample with x=0.01 appears a large magnetic entropy ΔSM=3.3 J kg-1 K-1 at the Curie temperature TC=274 K, which may be used as a promising candidate for magnetic refrigerant near room temperature. [ABSTRACT FROM AUTHOR]

Single phases of double layered perovskitelike Sr2-xGdxFeMoO6 samples with x varying from 0.00 to 0.25 have been synthesized. Distortion in FeO6 and MoO6 octahedrons is characterized by Rietveld refinements using the powder x-ray diffraction data. Antisite defects are considered during the refinements. Positron annihilation spectroscopy shows us that the density of antisite defects increases with increasing x. The size of defects reaches the largest values, and conducting electrons are most extensive in sample with x=0.20. The insulating behavior is observed. We argue that the valence states between Fe and Mo play the critical role in magnetism and transition properties in Gd doped Sr2FeMoO6. [ABSTRACT FROM AUTHOR]

We introduce enhanced hybridization of Ti 3d-O 2p electronic states by applying an inhomogeneous electric field to a perovskite oxide, SrTiO3, which leads to lattice deformation through electrostriction and the converse flexoelectric effect. However, unlike most studies revealing lattice responses to dipolar polarization, the enhanced electronic hybridization introduced in SrTiO3 is not strong enough to compensate local repulsions and gives rise to the off-centered Ti displacement. This is consistent with the fact that SrTiO3 has a small vibronic coupling constant compared to other ferroelectric materials. In situ time-dependent X-ray diffraction studies reveal lattice relaxation. Band structures and electronic hybridization play important roles in lattice relaxation, which is different from the relaxation of metals where the carrier concentration may be dominant. Our results provide insight into the coupling behaviors between the lattice and electronic hybridization, considering both static and dynamic aspects. [ABSTRACT FROM AUTHOR]

The heterostructure La[sub 0.67]Ca[sub 0.33] MnO[sub 3]/YBa[sub 2]Cu[sub 3] O[sub 7-δ] (LCMO/YBCO) bilayers with a fixed LCMO thickness and varying YBCO thickness were deposited on (001)-oriented single crystal SrTiO[sub 3] (STO) substrate and its resistivity properties were investigated by standard four-probe technique without magnetic field applied. The X-ray diffraction (XRD) analysis shows that all the bilayers were well c-oriented grown. The resistivity measurement indicated that the bilayer's properties change from superconductivity to magnetism with the decrease of the thickness of the capping layer YBCO. There exists a critical thickness of YBCO, in which case the superconductivity and magnetism coexist in bilayer. We believe that the lattice strain and spin-polarized carriers injection are the main origin of the above-mentioned resistivity behavior. [ABSTRACT FROM AUTHOR]

The effects of Sc in high Tc superconductors are seldom discussed due to the difficulty of Sc embedding into the unit cell. Single phase of Y1-xScxBa2Cu3O7-δ (YSBCO) is obtained with x<0.15. The critical current (Jc) varies with the content of Sc in an oscillating way, which has showed two maximum values at x=0.03 and x=0.10, individually. We here discussed the effect of Sc doping on Jc. [ABSTRACT FROM AUTHOR]

A double buffer of EU2CuO3/YSZ has been used to grow highly epitaxial thin films of YBa2Cu3Oy (YBCO) on Si. These films showed enhanced superconductivity and improved crystallinity in comparing with that of films grown on Si directly. Well defined interfaces with no immediate layers were found. The YBCO film surface was more smooth and stable. The results obtained indicate that highly epitaxial YBCO thin films can be successfully grown on Si wafers, demonstrating advantages of such a double buffer structure. [ABSTRACT FROM AUTHOR]

The polycrystalline samples of La2/3Ca1/3Mn1-xCoxO3 (LCMCO) (x ≤ 0.20) with single phase are synthesized by solid-state reaction method. Rietveld refinements proved that Co replaces Mn in LCMCO. The lattice parameters decrease monotonically with increasing Co content, while the bond angles of Mn-O-Mn increases from 160.4° (x = 0.02) to 170.2° (x = 0.20). The metal-to-insulator transition temperature decreases with increasing Co content. The scattering of coupling between eg electrons and the surface phonons, which is indicated by Tp, decreases with the increase of Co content. Magne-toresistance at TMI decreases with increasing the Co content from 297.4% to 81.4%, but increases at Tp from 23.8% to 121.2%, respectively. [ABSTRACT FROM AUTHOR]

Single phases of double layered perovskitelike Sr2-xGdxFeMoO6 samples with x varying from 0.00 to 0.25 have been synthesized. Distortion in FeO6 and MoO6 octahedrons is characterized by Rietveld refinements using the powder x-ray diffraction data. Antisite defects are considered during the refinements. Positron annihilation spectroscopy shows us that the density of antisite defects increases with increasing x. The size of defects reaches the largest values, and conducting electrons are most extensive in sample with x=0.20. The insulating behavior is observed. We argue that the valence states between Fe and Mo play the critical role in magnetism and transition properties in Gd doped Sr2FeMoO6. [ABSTRACT FROM AUTHOR]

We introduce enhanced hybridization of Ti 3d-O 2p electronic states by applying an inhomogeneous electric field to a perovskite oxide, SrTiO3, which leads to lattice deformation through electrostriction and the converse flexoelectric effect. However, unlike most studies revealing lattice responses to dipolar polarization, the enhanced electronic hybridization introduced in SrTiO3 is not strong enough to compensate local repulsions and gives rise to the off-centered Ti displacement. This is consistent with the fact that SrTiO3 has a small vibronic coupling constant compared to other ferroelectric materials. In situ time-dependent X-ray diffraction studies reveal lattice relaxation. Band structures and electronic hybridization play important roles in lattice relaxation, which is different from the relaxation of metals where the carrier concentration may be dominant. Our results provide insight into the coupling behaviors between the lattice and electronic hybridization, considering both static and dynamic aspects. [ABSTRACT FROM AUTHOR]

Ruthenium-based perovskite systems are attractive because their structural, electronic, and magnetic properties can be systematically engineered. The SrRu03/SrTi03 superlattice, with its period consisting of one unit cell each, is very sensitive to strain change. Our first-principles simulations reveal that, in the high tensile strain region, it transits from a ferromagnetic metal to an antiferromagnetic insulator with clear tilted octahedra, while in the low strain region, it is a ferromagnetic metal without octahedra tilting. Detailed analyses of three spin-down Ru - t2g orbitals just below the Fermi level reveal that the splitting of these orbitals underlies these dramatic phase transitions, with the rotational force constant of Ru06 octahedron high up to 16 meV/Deg2, 4 times larger than that of Ti06. Differently from nearly all the previous studies, these transitions can be probed optically through the diagonal and off-diagonal dielectric tensor elements. For a 1% change in strain, our experimental spin moment change is --0.14 ± 0.06 fiB, quantitatively consistent with our theoretical value of --0.1 pB. [ABSTRACT FROM AUTHOR]

The polycrystalline samples of La2/3Ca1/3Mn1-xCoxO3 (LCMCO) (x ≤ 0.20) with single phase are synthesized by solid-state reaction method. Rietveld refinements proved that Co replaces Mn in LCMCO. The lattice parameters decrease monotonically with increasing Co content, while the bond angles of Mn-O-Mn increases from 160.4° (x = 0.02) to 170.2° (x = 0.20). The metal-to-insulator transition temperature decreases with increasing Co content. The scattering of coupling between eg electrons and the surface phonons, which is indicated by Tp, decreases with the increase of Co content. Magne-toresistance at TMI decreases with increasing the Co content from 297.4% to 81.4%, but increases at Tp from 23.8% to 121.2%, respectively. [ABSTRACT FROM AUTHOR]