Ti-rich Samples Research Articles

Elemental effect on the phase formation and mechanical properties in the FeNiMnCuAlTi alloy system

The FeNiMnCuAlTi alloys were prepared using the arc-melting method by varying the individual elements. The change in microstructure and mechanical properties of the alloys due to the changes in the elemental composition was carried out by X-ray diffraction, Scanning Electron Microscopy, and transmission electron microscopy. Equiatomic composition exhibited the B2_BCC and C_14 Laves phase, whereas increasing the Fe content in the alloys enhanced the formation of the BCC phase. Cu and Ni enhanced the formation of the FCC phase and the addition of Al and Ti favored the formation of intermetallics. Cu tends to segregate in the inter-dendritic region in all these alloys by forming a Cu-Mn-rich FCC phase. Fe, Ni, Cu and Mn-rich alloys showed good plasticity, whereas Al and Ti-rich samples are extremely brittle. A high compressive yield strength of 2016 MPa, 1526 MPa, and 1255 MPa was observed for the high-entropy alloys Fe30(NiMnCuAlTi)70, Ni30(FeMnCuAlTi)70, and Mn30(NiFeCuAlTi)70 respectively, with plasticity varying between 3% to 10%. Whereas medium entropy alloys showed a lower compressive yield strength but with increased plasticity e.g., a compressive yield strength of 1525 MPa and 27% plasticity for the case of Fe50(NiMnCuAlTi)50 was observed. The good combination of strength and plasticity is due to the presence of the FCC/BCC phase with a fine uniform distribution of intermetallic phases.

High-sensitive XANES analysis at Ce L2-edge for Ce in bauxites using transition-edge sensors: Implications for Ti-rich geological samples

Accurate determination of cerium (Ce) valence state is important for interpreting the Ce anomaly in geological archives for (paleo)redox reconstruction. However, the routine application of Ce L3-edge X-ray absorption near-edge structure (XANES) spectroscopy for detecting trace Ce in geological samples can often be restricted by coexisting titanium (Ti) due to the proximity of their fluorescence emission lines. Therefore, the signal-to-noise ratio of Ce L3-edge XANES spectra may not be sufficiently high for high-quality spectroscopic analysis. This study introduces a semi-quantitative approach appropriate for Ti-rich, Ce-dilute geological materials by synchrotron-based X-ray measurement at the Ce L2-edge. First, the results confirm that Ce L2-edge XANES spectra are able to avoid overlapping Ti Kβ emissions and provide more reliable information on the Ce valence state in Ti-rich materials relative to L3-edge XANES. Moreover, the application of transition-edge sensor (TES) could reach the higher sensitivity with better energy resolution than conventional silicon drift detector (SDD) to detect fluorescence X-ray (Ce Lβ1). The investigation on bauxites developed from the Columbia River Basalts shows that combining Ce L2-edge XANES and TES allows for resolving weak Ce fluorescence lines at the L2-edge from Ti-rich, Ce-dilute samples (Ti/Ce mass ratio up to ∼6000, tens of ppm Ce). The outcome emphasizes the practical possibility of investigating Ce redox state in Ti-rich geological samples.

TiAl-based semi-finished material produced by reaction annealing of Ti/Al layered composite sheets

In this study multi-layered Ti/Al sheets prepared by accumulative roll bonding (ARB) underwent a two-step heat treatment (HT) to form intermetallic compounds. The microstructure and crystal structure of the samples were examined by scanning and transmission electron microscopy as well as energy-dispersive X-ray spectroscopy and synchrotron diffraction. In the first solid-state reaction annealing step, Ti-rich ARB samples containing 60 at% Ti and 40 at% Al were held at 600 °C for 12 h under a uniaxial pressure between 0 MPa and 50 MPa applied along the normal direction of the sheets. At this stage, Al is completely consumed by forming mainly Al-rich intermetallic phases and to a lower extent other titanium aluminides such as Ti3Al and TiAl. In the second step, high-temperature annealing produces TiAl and Ti3Al as major phases during both pressureless annealing at 1100 °C, 1200 °C and 1300 °C and annealing under an uniaxial pressure of about 100 MPa at 1200 °C. Pore formation during the reaction annealing can be significantly reduced by the applied pressure. As a result, a TiAl-based semi-finished material was fabricated.

Effect of ammonium salt on the distribution of titanium species in the synthesis of TS-1 zeolites

Titanium silicalite (TS-1) zeolites with different distribution of Ti species were synthesized through altering different amounts of (NH4)2SO4 as crystallization-mediating agent. The distribution of titanium species of TS-1-X samples (X represents the molar ratio of (NH4)2SO4 to SiO2) was systematically investigated via ICP-AES, FT-IR, UV-vis, UV-Raman and other techniques. The TS-1-X zeolite samples were applied in the epoxidation of 1-hexene reaction. It was found that the appropriate amount of ammonium salt not only facilitated the enrichment of titanium species from liquid phase to solid phase and promoted the incorporation of Ti into the MFI skeleton, but also resulted in the formation of uniformly small TS-1 crystals due to the inhibition of rapid growth of crystals. However, much more amounts of (NH4)2SO4 led to the formation of extra-framework Ti, including anatase TiO2 and amorphous Ti species. Meanwhile it promoted the rapid growth of grain resulting in larger TS-1 crystals. Ti-rich TS-1 sample synthesized with molar ratio of (NH4)2SO4 to SiO2 of 0.2 exhibited higher conversion of 1-hexene (42%) and effective utilization of H2O2 (81.8%). In addition, the effect of ammonium salt's composition on the properties of TS-1 was investigated by experiments and characterizations. It was found that ammonium salt could regulate the process of crystallization through its own anion and changing pH of the synthesis gel.

Microstructure and strengthening mechanism of boride in-situ reinforced titanium matrix composites prepared by plasma activated sintering

In this study, titanium matrix composites (TMCs) were prepared by plasma activated sintering. The microstructure and mechanical properties of the composites were studied, and the strengthening mechanism was determined. The results showed that the main phases of Ti-rich samples are TiB, α-Ti and β-Ti, while the primary phases of TiB2-rich samples are TiB2 and TiB. The composites containing 70 wt%TC4-30 wt%TiB2 demonstrated the best performance which achieved a balance of high strength and ductility, with a yield strength of 1800 ± 28 MPa and compressive strength of 2215 ± 39 MPa. The key reinforcing and toughening mechanisms were due to the dislocation defects and stacking faults in the samples, which consume more fracture energy during crack propagation and comprehensively improve the strength and toughness of the composites. Furthermore, crack deflection and whisker pull-out caused by TiB can toughen the composites.

Modulation of the electric and magnetic properties by Ti non-stoichiometry in 0.70BiFeO3-0.30BaTixO3 ceramics

The modulation of the structure and dielectric, ferroelectric, and magnetic properties by Ti non-stoichiometry in 0.70BiFeO3-0.30BaTixO3 (BF30BT-x, x = 0.85–1.15) ceramics was studied systematically. In Ti-rich samples, excessive Ti mainly exists in the form of an impurity Aurivillius phase, and so except that the impurity phase reduces the resistance, the structure, morphology, Curie temperature (TC ∼ 390 °C), and ferroelectricity in Ti-rich ceramics are similar to those in stoichiometric ceramics (BF30BT-1.00). In Ti-poor samples, the appropriate Ti-poor concentration appears in the BF30BT-0.90 ceramic, and the structure becomes the coexistence of the rhombohedral phase and the pseudo-cubic phase (R+PC). The ferroelectric phase transition becomes a frequency-independent normal phase transition, and TC is greatly increased (553 °C). The hysteresis loop becomes more saturated, and a large internal bias field (Ei = 4.5 kV/cm) appears. For magnetic properties, all samples display a weak ferromagnetic nature, and as x increases, Mr and Mmax increase nearly linearly.

The role of titanium on the microstructure and mechanical properties of additively manufactured C300 maraging steels

In this study, C300 metal powders containing two different Ti contents (0.72 and 1.17 wt%) were used to additively manufacture maraging steel samples in both horizontal and vertical directions via laser powder bed fusion (LPBF) technique. The effect of Ti addition on the microstructural and mechanical properties of the additively manufactured (AM) maraging steels was investigated using scanning, transmission electron microscopies (SEM, TEM), and electron backscatter diffraction (EBSD) along with uniaxial tensile and hardness testing procedures. Besides, X-ray diffraction (XRD) technique was employed to identify various phases formed during the LPBF process. The results showed that the horizontally printed Ti-rich samples exhibited higher retained austenite (γ) phase and superior values of hardness and tensile strength, while those ones vertically prepared showed an excellent ductility that could bring benefits in high-cycle fatigue applications. The TEM observations confirmed the presence of CoNi precipitates as well as high dislocation densities in the horizontal high Ti content samples, which are associated with higher strain hardening and tensile strength.

Impact of Ba/Ti ratio on the magnetic properties of BaTiO3 ceramics

Bulk BaTiO3 ceramics are prepared by solid state reaction route by varying Ba/Ti ratio from 0.990 to 1.005 in steps of 0.005 to study the influence of Ba/Ti ratio on the origin of ferromagnetism in the otherwise diamagnetic material. Structural investigation confirmed the coexistence of two-phase structural model, tetragonal (P4mm) + orthorhombic (Amm2) using Rietveld refinement program. For the first time, structural defect of Ti vacancies are quantified using refinement while the Ba and O are fully occupied. Room temperature magnetic M-H measurements have indicated that the diamagnetic-like and ferromagnetic-like loops in Ti-rich and Ti-deficient BaTiO3 system respectively. The ferromagnetic-like behavior (Ti-deficient) is originated from the intrinsic defect that is Ti vacancy which plays a decisive role in the magnetic property of otherwise diamagnetic BaTiO3 ceramics. Magnetodielectric constant is negligible in Ti-rich samples while high value of magnetodielectric constant is obtained as – 0.88% at 0.8T in Ba/Ti = 1.005 sample.

Defect chemistry and dielectric behavior of Sr0.99Ce0.01Ti1−xO3 ceramics with high permittivity

Sr0.99Ce0.01Ti1-xO3 (SCT, x = 0, ± 0.0025, ± 0.0050, 0.0075) ceramics were prepared by solid state reaction methods and sintered in air atmosphere at different temperatures, with a soaking time of 2 h. The dielectric properties of all samples presented excellent temperature independence over a broad temperature range from 25 to 330 ℃ and frequency independence between 10 kHz and 1 MHz. Sr0.99Ce0.01Ti0.9925O3 (SCT0.9925) ceramics sintered in air atmosphere exhibited a high permittivity (~5400) and a low dielectric loss (~0.01) measured at room temperature and 1 kHz. XPS and complex impedance spectroscopy analysis confirmed that the high permittivity and low dielectric loss were attributed to the fully ionized oxygen vacancies and giant defect-dipoles in Ti-deficient samples. However, a higher dielectric loss of Ti-rich samples is owing to the destruction of giant defect dipoles, in which highly localized electrons were transformed into hopping electrons.

The influence of non-stoichiometry on the switching kinetics of strontium-titanate ReRAM devices

Compared to conventional NAND flash resistive switching metal-oxide cells show a number of advantages, like an increased endurance, lower energy consumption, and superior switching speed. Understanding the role of defects for the resistive switching phenomenon in metal oxides is crucial for their improvement and thereby also for their acceptance as a next generation data storage device. Strontium titanate (STO) is considered a model material due to its thoroughly investigated defect chemistry. This paper presents a comparative study of the switching kinetics for three different compositions [Sr]/([Sr]+[Ti]) of 0.57 (Sr-rich), 0.50 (stoichiometric STO), and 0.46 (Ti-rich STO). The STO films, deposited by atomic layer deposition, were integrated in Pt/STO/TiN nanocrossbars with a feature size of 100 nm. By analysis of the transient currents, the switching kinetics are investigated between 10 ns and 104 s for the SET and 10 ns and 100 s for the RESET. A clear influence of the composition on the degree of nonlinearity of the switching kinetics was observed. Applying an analytical model for the oxygen vacancy migration, we were able to explain the differences in the SET kinetics by composition-dependent changes in the thermal conductivity and by a lower activation energy for the Ti-rich sample. This might be utilized in design rules of future ReRAM devices.

The competitive growth of cubic domains in Ti(1-x)AlxN films studied by diffraction anomalous near-edge structure spectroscopy.

Titanium and aluminium nitride films deposited by magnetron sputtering generally grow as columnar domains made of oriented nanocrystallites with cubic or hexagonal symmetry depending on Al content, which are embedded in more disordered grain boundaries. The substitution of Al atoms for Ti in the cubic lattice of the films improves their resistance to wear and oxidation, allowing their use as protective coatings. Ti K-edge X-ray absorption spectroscopy, which probes both crystallized and more disordered grain boundaries, and X-ray diffraction anomalous fine structure, which is sensitive to short- and long-range order within a given crystallized domain, are carried out on a set of Ti(1-x)AlxN films deposited by magnetron sputtering on Si substrates. Attention is paid to the shape of the pre-edge region, which is sensitive to the symmetry of the site occupied by Ti atoms, either octahedral in face-centred-cubic Ti-rich (TiN, Ti0.54Al0.46N) samples or tetrahedral in hexagonal-close-packed Al-rich (Ti0.32Al0.68N) films. In order to obain information on the titanium environment in the well crystallized areas, subtraction of the smooth part of the energy-dependent structure factor for the Bragg reflections is applied to the pre-edge region of the diffraction anomalous data in order to restore their spectroscopic appearance. A flat pre-edge is related to the typical octahedral environment of Ti atoms for cubic reflections. The difference observed between pre-edge spectra associated with face-centred-cubic 200 and 111 Bragg reflections of Ti0.54Al0.46N is assigned to Ti enrichment of 111 large well ordered domains compared with the more disordered 200 ones. The sharp peak observed in the spectrum recorded from the hexagonal 002 peak of Ti0.32Al0.68N can be regarded as a standard for the pure tetrahedral Ti environment in hexagonal-close-packed nitride.

Evaluation of Rh/CexTi1−xO2 catalysts for synthesis of oxygenates from syngas using XPS and TPR techniques

Rh/CexTi1−xO2 catalysts have been investigated for the synthesis of ethanol from syngas. For this purpose various CexTi1−xO2 (x=0, 0.25, 0.5, 0.75, and 1) solid solution supports were synthesized using co-precipitation, which is an inexpensive and environmental friendly method. 2wt% Rh has been deposited over these supports by using wet impregnation method. We have evaluated these Rh catalysts for synthesis of ethanol from syngas at atmospheric pressure and 350psi. Among, the various catalysts, Rh supported on Ce0.75Ti0.25O2 catalyst exhibit better selectivity toward oxygenates compared to other catalysts. Interestingly, Ti rich samples exhibit higher selectivity toward hydrocarbons while Ce rich samples exhibit higher selectivity toward oxygenated products. The catalytic results at atmospheric pressure show that titania rich catalysts exhibit higher H2 conversion and ceria rich catalysts exhibit higher CO-conversion at 250°C at atmospheric pressure. Temperature programmed reduction measurements suggest that Rh promotes the cerium surface reduction. X-ray photoelectron measurements show that all the catalysts exhibit peaks due to Ce4+ and Ce3+ oxidations states in the Ce 3d spectra. O1s spectra of activated Rh/TiO2 and Rh/Ce0.5Ti0.5O2 catalysts show two peaks after reduction in hydrogen. One peak is due to the oxygen atoms from the individual oxides and the other peak is from the compound formation between Rh and the support. X-ray photoelectron measurements of activated catalysts also show that Rh/Ce0.5Ti0.5O2 catalyst exhibit higher Rh1+ ions on the surface compared to Rh/TiO2 and exhibits better selectivity toward oxygenated products.

Reactive synthesis and characterization of titanium aluminides produced from elemental powder mixtures

The formation of titanium aluminides in Ti–Al elemental powder mixtures containing 25, 50 and 75 at.% Al, has been studied using differential scanning calorimetry (DSC). Phase evolution in the mixture was followed by heating the compacted samples up to 1273 K at 7.5 and 15 K min−1. The cooled samples were characterized using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. The results showed that the primary combustion product in all the samples was TiAl3, and the combustion reaction occurred below the melting point of aluminum only in Ti-rich samples. In Al-rich samples (75 at.% Al), TiAl3 was obtained as a porous, single-phase product after combustion. In samples containing 25 and 50 at.% Al, the combustion reaction was incomplete and the unreacted titanium particles were covered by a layer of TiAl3. In these samples, other intermetallic compounds such as TiAl2, TiAl and Ti3Al were observed to form upon heating beyond the combustion peak and are attributed to the solid-state reaction between unreacted titanium and TiAl3. Heating the samples with 25 at.% Al to 1273 K for an hour led to the formation of a homogenous Ti3Al product, while a multiphase product with a dominant TiAl phase was observed in samples containing 50 at.% Al. Calculations based on DSC data show that the formation of TiAl3 through the reaction between solid titanium and molten aluminum is associated with an apparent activation energy of 195 ± 20 kJ mol−1 and an enthalpy of −114 ± 5 kJ mol−1.

Ti-RICH ANDRADITES: CHEMISTRY, STRUCTURE, MULTI-PHASES, OPTICAL ANISOTROPY, AND OSCILLATORY ZONING

Electron probe microanalyzer (EPMA) data were obtained for 11 Ti-rich andradite garnet, [8] X 3 [6] Y 2 [4] Z 3 [4] O 12 , samples from Magnet Cove, Arkansas, USA. The crystal structures of nine of these samples were refined with the Rietveld method, space group la¯ 3 d , and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. One sample (MC9) contains two distinct compositions corresponding to different phases and subtle compositional differences are observed in two other samples (MC8 and MC10). The EPMA data falls on a straight line representing solid solutions from the endmember andradite, Ca 3 Fe 3+ 2 Si 3 O 12 , to a composition, Ca 3 (Ti 4+ 1.5 Fe 2+ 0.5 )[Fe 3+ Si 2 ]O 12 , with the coupled substitution: Fe 3+ + Si 4+ ↔ Ti 4+ 1.5 + Fe 2+ 0.5 . The Y site contains Ti 4+ cations (up to ≈1.1 atom per formula unit, apfu ). A few samples show oscillatory zoning that arises mainly from the distribution of Ti atoms coupled with subtle variations in Fe, Al, and Mg atoms. The HRPXRD results show that seven samples contain two or three cubic phases intergrown together. These seven samples exhibit birefringence because of strain arising from structural mismatch. There are three Ti-rich schorlomite samples (MC1, MC5, and MC7) of which MC1 and MC7 are single cubic phases and are isotropic. The bond distances (average , Y–O, Z–O, and mean ) change linearly with increasing a unit-cell parameter. The Y–O distance is nearly constant. The Z–O distance increases most because of Fe 3+ (0.49 A) substituting for Si 4+ (0.26 A) cations at the Z site.

Formation of M<sub>5</sub>Si<sub>3</sub> Type Si-Ti-Zr System Intermetallic Compounds by Pulse Electric Current Sintering with Self-Propagating High Temperature Synthesis

Pulse electric current sintering (PECS) is applied to synthesis M5Si3 type Si-Ti-Zr system intermetallic compounds, Si3TixZr(5-x) x=0-5, directly from raw powders of silicon, titanium and zirconium. Almost full conversion to Si3TixZr(5-x) are achieved by PECS method with self-propagating high temperature synthesis (SHS) reaction. The adiabatic temperatures are susceptible to sintering behaviors such as vacuum pressure in chamber and displacement of pressure axis on the PECS process. The large quantities of gases are released in Zr-rich samples. The bulk shapes with almost dense samples are obtained at Ti-rich samples.

Microbeam X-ray analysis of Ce3+/Ce4+ in Ti-rich minerals: A case study with titanite (sphene) with implications for multivalent trace element substitution in minerals

Cerium L 3 absorption edge ( L 3-edge) X-ray absorption near edge structure (XANES) spectra were obtained from ~7 × 5 μm areas on green titanite and brown titanite (both with total Ce ~ 0.6 wt%) using the X-ray microprobe at the Pacific Northwest Consortium–X-ray Science Division (PNC-XSD) Insertion Device (ID) line of the Advanced Photon Source (APS). Using a wavelength-dispersive X-ray (WDX) fluorescence detector with a bent LiF (220) crystal monochromator ( E /Δ E ~ 1000), we have overcome the challenge of having to measure trace amounts of Ce in a Ti-rich sample of which the energy of the fluorescence X-rays from Ce L 3-edge and Ti K -edge excitation cannot be resolved with solid-state detectors. We show that both Ce3+ and Ce4+ are present in our titanite samples by examining the Ce L 3-edge XANES spectra. Our results show that to correctly determine trace element substitution mechanisms in titanite (and other minerals), it is necessary to determine multivalent element concentrations, including Ce3+/Ce4+. We present a new approach for predicting and evaluating multivalent trace element substitution in titanite and other minerals.

Search for Ti–Ni–Zr thin film metallic glasses exhibiting a shape memory effect after crystallization

Abstract We conducted a search for Ti–Ni–Zr thin film metallic glasses (TFMGs) exhibiting a shape memory effect after crystallization. We investigated the possibility of (Ti, Zr)(100−x)–Nix thin film amorphous alloys exhibiting a glass transition. All prepared samples were classified into three groups such as Ti-rich (x 51) samples. Equiatomic Ti–Ni–Zr thin film amorphous alloys with Zr content ranging from 11 to 17 at.% showed a glass transition, and thus were concluded to be TFMGs. Several Ni-rich samples exhibit glass transition and were also TFMGs. On the other hand, Ti-rich samples did not exhibit a glass transition irrespective of the Zr content. Moreover, we investigated the shape memory behavior of crystallized TiNiZr TFMGs. Ti39Ni50Zr11 TFMGs annealed at 973 K for 3.6 ks exhibited a martensitic transformation from the B2 to the B19′ phase upon cooling and heating. The martensitic phase start temperature and reverse martensitic phase start temperature were 296 and 352 K, respectively. In addition, this alloy showed good shape memory behavior, achieving recovery strain of 2.5% and a critical stress for slip of 500 MPa.

The oxygen isotope composition, petrology and geochemistry of mare basalts: Evidence for large-scale compositional variation in the lunar mantle

To investigate the formation and early evolution of the lunar mantle and crust we have analysed the oxygen isotopic composition, titanium content and modal mineralogy of a suite of lunar basalts. Our sample set included eight low-Ti basalts from the Apollo 12 and 15 collections, and 12 high-Ti basalts from Apollo 11 and 17 collections. In addition, we have determined the oxygen isotopic composition of an Apollo 15 KREEP (K – potassium, REE – Rare Earth Element, and P – phosphorus) basalt (sample 15386) and an Apollo 14 feldspathic mare basalt (sample 14053). Our data display a continuum in bulk-rock δ 18O values, from relatively low values in the most Ti-rich samples to higher values in the Ti-poor samples, with the Apollo 11 sample suite partially bridging the gap. Calculation of bulk-rock δ 18O values, using a combination of previously published oxygen isotope data on mineral separates from lunar basalts, and modal mineralogy (determined in this study), match with the measured bulk-rock δ 18O values. This demonstrates that differences in mineral modal assemblage produce differences in mare basalt δ 18O bulk-rock values. Differences between the low- and high-Ti mare basalts appear to be largely a reflection of mantle-source heterogeneities, and in particular, the highly variable distribution of ilmenite within the lunar mantle. Bulk δ 18O variation in mare basalts is also controlled by fractional crystallisation of a few key mineral phases. Thus, ilmenite fractionation is important in the case of high-Ti Apollo 17 samples, whereas olivine plays a more dominant role for the low-Ti Apollo 12 samples. Consistent with the results of previous studies, our data reveal no detectable difference between the Δ 17O of the Earth and Moon. The fact that oxygen three-isotope studies have been unable to detect a measurable difference at such high precisions reinforces doubts about the giant impact hypothesis as presently formulated.

Thermal stability of TiN metal gate prepared by atomic layer deposition or physical vapor deposition on HfO2 high-K dielectric

In this paper, the thermal stability of TiN metal gate with various composition prepared by different preparation technology [(e.g., atomic layer deposition (ALD) or physical vapor deposition (PVD)] on HfO2 high-K dielectric is investigated and compared by physical and electrical analysis. After annealing of the TiN/HfO2 stack at 1000 °C for 30 s, it is observed that: (1) Nitrogen tends to out-diffuse from TiN for all the samples; (2) Oxygen from the interfacial layer (IL) between HfO2 and Si tends to diffuse toward TiN. PVD Ti-rich TiN shows a wider oxygen distribution in the gate stack, and a thinner IL than the N-rich sample. Ti penetration into HfO2 is also observed in the Ti-rich sample, which can potentially lead to the dielectric break-down. Besides, the oxygen out-diffusion can be significantly suppressed for ALD TiN compared to the PVD TiN samples.

Superconductivity in a new iron pnictide oxide(Fe2As2)(Sr4(Mg, Ti)2O6)

We have discovered a new iron pnictide oxide superconductor(Fe2As2)(Sr4(Mg, Ti)2O6). This material isisostructural with (Fe2As2)(Sr4M2O6) (M = Sc, Cr, V),which were found in previous studies. The structure of this compound is tetragonal with a space group ofP4/nmm andconsists of the anti-fluorite type FeAs layer and perovskite-type block layer. The lattice constants area = 3.935 Å andc = 15.952 Å for(Fe2As2)(Sr4MgTiO6). Bulk superconductivitywith a Tc(onset) of ∼ 26 K was observed for a partially Co-substituted sample. Moreover, Co-free and Ti-rich samples exhibitedhigher Tc(onset)s above 35 K, which were further enhanced by applying high pressures up to ∼ 43 K.