Zr Ratio Research Articles

Enhanced Thermoelectric Performance in Hf-Free p-Type (Ti, Zr)CoSb Half-Heusler Alloys

High thermal conductivity and exorbitant cost of Hf has for a long time limited the prospects of half-Heusler (HH) alloys for applicability in thermoelectric (TE) energy conversion devices. This work demonstrates the implication of nanostructuring and efficacy of p-type acceptor dopant in (Ti,Zr)CoSb based HH alloys for enhancing the figure of merit (ZT) while eliminating the use of Hf. A series of (Ti,Zr)CoSb1−x(Si,Sn)x HH composition was synthesized using arc-melting and consolidated employing spark plasma sintering (SPS). The optimal doping of acceptor dopants, namely, Si and Sn significantly improves the power factor and strengthens the phonon scattering resulting in an enhanced TE performance with maximum ZT of 0.26 and 0.5 at 873 K, obtained for TiCoSb0.8Sn0.2 and ZrCoSb0.8Sn0.2, respectively. For further optimization, microstructural modifications by fine-tuning of the Ti to Zr ratio induces strain field effects and mass fluctuation in (Ti,Zr)CoSb0.8Sn0.2 compositions, which remarkably introduces additional phonon scattering resulting in maximum ZT ∼ 0.8 at 873 K for the best performing Zr0.5Ti0.5CoSb0.8Sn0.2 compound. The current study provides a better understanding of p-type dopants in HH materials by which prospective high TE performance can be obtained in low-cost Hf-free p-type (Ti,Zr)CoSb half-Heusler alloys.

Physical and chemical transformations of zirconium doped ceria nanoparticles in the presence of phosphate: Increasing realism in environmental fate and behaviour experiments

During their lifecycle, many engineered nanoparticles (ENPs) undergo significant transformations that may modify their toxicity, behaviour, and fate in the environment. Therefore, understanding the possible environmentally relevant transformations that ENPs may undergo as a result of their surroundings is becoming increasingly important. This work considers industrially produced ceria (CeO2) and focuses on a particle library consisting of seven zirconium-doped variants (Ce1-xZrxO2) where the Zr doping range is x = 0–1. The study assesses their potential transformation in the presence of environmentally relevant concentrations of phosphate. These ENPs have an important role in the operation of automotive catalysts and therefore may end up in the environment where transformations can take place. Samples were exposed to pH adjusted (c. 5.5) solutions made up of either 1 mM or 5 mM each of KH2PO4, citric acid and ascorbic acid and the transformed particles were characterised by means of DLS – size and zeta potential, UV/VIS, TEM, FT-IR, EDX and XRD. Exposure to the phosphate solutions resulted in chemical and physical changes in all ceria-containing samples to cerium phosphate (with the monazite structure). The transformations were dependent on time, ceria concentration in the particles (Ce:Zr ratio) and phosphate to ceria ratio. The presence of Zr within the doped samples did not inhibit these transformations, yet the pure end member ZrO2 ENPs showed no conversion to phosphate. The quite dramatic changes in size, structure and composition observed raise important questions regarding the relevant form of the materials to investigate in ecotoxicity tests, and for regulations based on one or more dimensions in the nanoscale.

Nanostructured Diatom-ZrO2 composite as a selective and highly sensitive enzyme free electrochemical sensor for detection of methyl parathion

In the current work we report a simple and scalable technique for synthesis of ordered nanoporous Si-ZrO2 composite derived from the diatom Phaeodactylum tricornutum. The composite was well characterized using SEM, TEM-EDX, FTIR, TGA, BET and DLS. The diatom-ZrO2 was found to have a specific surface area of 140 m2/g, Si:Zr ratio of 1:4 and a particle size of 80 ± 2 nm. This composite was evaluated as an enzyme free electrochemical sensor towards the detection of methyl parathion (MP) and showed excellent sensing ability at extremely low detection limits of 54.3 pM and a linear concentration range of 3.4 nM to 64 μM. The diatom-ZrO2 composite was also found to be highly selective towards MP as shown by its response even in the presence of high concentrations of other interfering molecules and ions.

Down- and up-conversion photoluminescence of ZrO2:Ho3+ and ZrO2:Ho3+/Yb3+ coatings formed by plasma electrolytic oxidation

This paper discusses ZrO2:Ho3+ and ZrO2:Ho3+/Yb3+ coating formation by the plasma electrolytic oxidation (PEO) of zirconium in alkaline electrolyte containing Ho2O3 and Ho2O3/Yb2O3 particles, respectively. The morphology, chemical and phase composition, as well as down- and up-conversion photoluminescence (PL) of the coatings, were investigated. Down-conversion PL emission spectra of ZrO2:Ho3+ excited by 280 nm radiation are composed of broad PL band associated with ZrO2 host and bands corresponding to f–f transitions of Ho3+. The main PL emission bands of Ho3+ at around 540 nm and 550 nm are assigned to 5F4→5I8 and 5S2→5I8 transitions, respectively. The down-conversion PL intensity of ZrO2:Ho3+ excited by 450 nm radiation (transition 5I8→5G6) strongly depends on the concentration of Ho3+ incorporated into ZrO2 coatings. That is, it depends on the duration of the PEO process and concentration of Ho2O3 particles in electrolyte. PL intensity increases with rising Ho3+ concentration in ZrO2 coatings, reaching a maximum Ho:Zr ratio of about 18⋅10−3 and shows concentration quenching for higher values. Excitation of ZrO2:Ho3+/Yb3+ coatings by 980 nm laser diode results in the appearance of a strong green (5F4,5S2→5I8), weaker red (5F5→5I8), and NIR (5F4,5S2→5I7) up-conversion emissions. An increase of the PL intensity with increasing Yb3+ concentration indicates an efficient transfer of energy from excited Yb3+ ions to Ho3+ ions.

Effective adsorption of phosphoric acid by UiO-66 and UiO-66-NH2 from extremely acidic mixed waste acids: Proof of concept

Streams of waste mixed acids from conventional wet etching processes contain high levels of H3PO4, which warrant recycling. This investigation is the first to use metal organic framework UiO-66 and UiO-66-NH2 to adsorb phosphoric acid from waste mixed acids from the world's largest semiconductor foundry, a synthetic HNO3H3PO4HAc mixture, and 85% phosphoric acid. Both UiO-66 and UiO-66-NH2 have high capacities to adsorb H3PO4 in extremely acidic solutions. The Langmuir adsorption capacities (qmax’s) of UiO-66 for waste mixed acids and a synthetic HNO3H3PO4HAc mixture on UiO-66 at 25 °C are 3360 and 8,510 mg-H3PO4/g, respectively, and that of 85% phosphoric acid on UiO-66 is 4,790 mg-H3PO4/g. The qmax of UiO-66-NH2 for phosphoric acid from 25% to 75% waste mixed acids is 4550 mg-H3PO4/g, which exceeds that of UiO-66. The corresponding P:Zr ratio for adsorbed MOF is in the range 6.2‒13.5, suggesting that the tested MOF crystals are super-adsorbents of phosphoric acid under extremely acidic conditions.

When binaries keep track of recent nucleosynthesis

Context. Barium stars are s-process enriched giants. They owe their chemical peculiarities to a past mass transfer phase. During this phase they were polluted by their binary companion, which at the time was an asymptotic giant branch (AGB) star, but is now an extinct white dwarf. Barium stars are thus ideal targets for understanding and constraining the s-process in low- and intermediate-mass AGB stars. Aims. We derive the abundances of a large number of heavy elements in order to shed light on the conditions of operation of the neutron source responsible for the production of s-elements in the former companions of the barium stars. Methods. Adopting a recently used methodology, we analyse a sample of eighteen highly enriched barium stars observed with the high-resolution HERMES spectrograph mounted on the Mercator telescope (La Palma). We determine the stellar parameters and abundances using MARCS model atmospheres. In particular, we derive the Nb–Zr ratio which was previously shown to be a sensitive thermometer for the s-process nucleosynthesis. Indeed, in barium stars, 93Zr has fully decayed into mono-isotopic 93Nb, so Nb/Zr is a measure of the temperature-sensitive 93Zr/Zr isotopic ratio. Results. HD 28159, previously classified as K5III and initially selected to serve as a reference cool K star for our abundance analysis, turns out to be enriched in s-process elements, and as such is a new barium star. Four stars are characterised by high nitrogen abundances, and among those three have high [Nb/Zr] and [hs/ls] ratios. The derived Zr and Nb abundances provide more accurate constraints on the s-process neutron source, identified to be 13C(α, n)16O for barium stars. The comparison with stellar evolution and nucleosynthesis models shows that the investigated barium stars were polluted by a low-mass (M ∼ 2 − 3 M⊙) AGB star. HD 100503 is potentially identified as a high metallicity analogue of carbon-enhanced metal-poor star enriched in both r- and s-process elements (CEMP-rs).

Ferroelectricity of HfxZr1−xO2 Thin Films Fabricated Using TiN Stressor and ZrO2 Nucleation Techniques

Recently, HfxZr1−xO2 (HZO) thin films have been widely investigated to achieve low power device applications such as ferroelectric random access memory (FeRAM) and ferroelectric field effect transistor (FeFET), due to its stable ferroelectricity even in extremely thin region (~10 nm) and CMOS applicability [1]. Moreover, matured atomic layer deposition (ALD) techniques of HfO2 and ZrO2 enable the fabrication of three-dimensional structure required for future memory devices. TiN top- and bottom-electrodes (TE- and BE-TiN) are typically used as stressor layers to fabricate metal-ferroelectric-metal (MFM) capacitors with HZO films because TiN electrodes provide the mechanical stress required for the formation of the unstable ferroelectric orthorhombic phase [2]. However, this method is suitable only for MFM capacitors, cannot be applied to FET structures. On the other hand, in our previous research, the HZO film fabricated using a polycrystalline ZrO2 nucleation layer, inserted between the HZO film and the BE-TiN, results in the large remanent polarization (2P r = P r + − P r −) [3]. Therefore, the HZO film with top- and bottom-ZrO2 nucleation layers is expected to improve the ferroelectricity. In this study, we fabricated two types of MFM capacitors with HZO films crystallized using top- and bottom-TiN stressor layers and ZrO2 nucleation layers, and discuss the ferroelectricity and the leakage current (J) properties of two types of MFM capacitors. The TiN/ZrO2/HZO/ZrO2/TiN capacitors with top- and bottom-ZrO2 nucleation layers (D-ZrO2) were fabricated as follows: A 2-nm-thick bottom-ZrO2 layer was deposited on the BE-TiN by ALD at 300°C using (C5H5)Zr[N(CH3)2]3 precursor and H2O gas. Next, a 10-nm-thick HZO film was deposited on the bottom-ZrO2 layer by ALD at 300°C using (Hf/Zr)[N(C2H5)CH3]4 (Hf/Zr = 1/1) cocktail precursor and H2O gas. A 2-nm-thick top-ZrO2 layer was then deposited on the HZO film using the same ALD conditions. After that, post-deposition-annealing (PDA) was carried out at 600°C for 1 min in a N2 atmosphere. Finally, TE-TiN was fabricated on the top-ZrO2 layer by DC sputtering. Two types of TiN/HZO/TiN capacitors with 10-nm-thick HZO films were also prepared as references. One is the capacitor annealed before TE-TiN deposition (w/o), the other is the capacitor annealed after TE-TiN deposition under the same annealing process (D-TiN). The Hf:Zr ratio in the HZO film was estimated to be 0.43:0.57 by energy dispersive x-ray spectroscopy analysis. Fig. 1 shows the polarization-electric field (P-E) hysteresis curves of w/o, D-TiN, and D-ZrO2. All of the capacitors exhibited hysteresis loops in the range from −3.0 to 3.0 MV/cm. The 2P r value was increased in the following order: w/o (12 µC/cm2) < D-TiN (24 µC/cm2) < D-ZrO2 (29 µC/cm2). The ratio of ferroelectric orthorhombic phase was increased in the following order: w/o < D-TiN < D-ZrO2, from x-ray diffraction patterns (not shown). Therefore, we determined that the top- and bottom-ZrO2 nucleation layers play an important role for the ferroelectric orthorhombic phase formation of HZO films. Fig. 2 shows the relationship between the J value at 1.0 V and the 2P r value of w/o, D-TiN, and D-ZrO2. For D-TiN case, the 2P r value was approximately 2.0 times larger than that of w/o probably due to the mechanical stress from TE-TiN. However, the J value of D-TiN was increased in the low voltage region compared to w/o. On the other hand, for D-ZrO2 case, the 2P r value was about 2.4 times larger than that of w/o. Moreover, the J value of D-ZrO2 was lower by one order of magnitude than that of D-TiN due to the larger thickness of D-ZrO2 than that of D-TiN. Based on these experimental results, the HZO films exhibited significantly superior ferroelectricity using double ZrO2 nucleation layers compared to that fabricated using double TiN stressor layers. This work was supported partly by Grant-in-Aid for JSPS Research Fellow and CREST, JST. [1] J. Müller et al., Appl. Phys. Lett. 99, 112901 (2011). [2] S. J. Kim et al., Appl. Phys. Lett. 111, 242901 (2017). [3] T. Onaya et al., Appl. Phys. Express 10, 081501 (2017). Figure 1

Evaluating the Efficiency of a Trace Amount of Zr Dopant on Photocatalytic Activity of TiO2 in Decolorization of Azo Dye

Zr-doped TiO2 nano photocatalyst obtained with a various trace amount of Zr, by using the sol-gel method. Several spectroscopic techniques applied to characterize the structures and properties of nano-photocatalyst. It founded that the effect of doping Zr ions to the TiO2 lattice led it to improve the surface properties and decreasing the particle size of nano-photocatalyst. Therefore, it causes increasing specific surface area and photocatalytic activity as compared with pure TiO2. The results revealed that there was an inverse relationship between the growth of the crystallite size of the nano photocatalyst and the decline of the molar ratios of Zr. The photocatalytic activity of the nano photocatalyst employed for the decolorization of Congo red as an Azo dye in the aqueous solution under UV irradiation in a batch reactor. The results exhibited that the TiO2/Zr0.0004 brings the best photocatalytic activity.

Determination of distribution ratios of Zr(IV), Co(II), Sb(V) and Nb(V) using polyaniline in acid solutions

In this work, we report the distribution ratios of Zr(IV), Co(II), Sb(V) and Nb(V) using polyaniline in HCl, HF, oxalic acid and HF + HCl solutions. Distribution ratios were determined by batch method using radiotracer technique. Further, the separation factors and the %-uptake of metal ions were calculated and compared. Among the media studied, separation factors for Co(II), Sb(V) and Nb(V) with respect to Zr(IV) were the highest in 1 M HCl and the values are 52, 108 and 404 respectively. The results of this study can be utilized for designing an ion-exchange process for the decontamination of zircaloy pressure tubes used in the Pressurized Heavy Water Reactors.

Facile non-aqueous synthesis of high color rendering C@ZrSiO4 encapsulation pigment with carbon-containing precursors as in-situ carbon sources

A zircon encapsulated carbon black (C@ZrSiO4) pigment with high color rendering was synthesized via facile non-aqueous acetic acid (NAA) assisted sol-gel method using carbon-containing precursors (zirconium n-propoxide and tetraethoxysilane) as in-situ carbon sources. The effects of the NAA amount and heat treatment temperature on the structure and properties of the synthesized encapsulation pigments were characterized by XRD, FT-IR, FE-SEM, HR-TEM, EDS, XPS and CIELAB colorimeter, respectively. The results showed that the C@ZrSiO4 encapsulated pigments heating at 1000 °C for 2 h in N2 atmosphere presented a dense and stable encapsulation structure as well as deep dark hue when the mole ratio of NAA and Zr (NAA/Zr) was 3:1, and the chromaticity values were L* = 21.20, a* = 0.56, b* = −0.09 and Cab = 0.57, respectively, which were contributed to the high homogeneity at atomic level in ZrSiO4 sol and the tight bonding between carbon black carbonized by carbon containing group and zircon matrix. In addition, the pigment exhibited excellent chemical stability, thermal stability and tinctorial strength when it was used in water, acid, alkali, organic solvents and ceramic glaze. Especially, these pigments improved the utilization of raw materials and avoided the use of heavy metals or transition metals as coloring agent, which was an environment-friendly black ceramic pigment.

Synthesis and characterization of Zr- and Hf-doped nano-TiO2 as internal standards for analytical quantification of nanomaterials in complex matrices.

The reliable quantification of nanomaterials (NMs) in complex matrices such as food, cosmetics and biological and environmental compartments can be challenging due to interactions with matrix components and analytical equipment (vials and tubing). The resulting losses along the analytical process (sampling, extraction, clean-up, separation and detection) hamper the quantification of the target NMs in these matrices as well as the compatibility of results and meaningful interpretations in safety assessments. These issues can be overcome by the addition of known amounts of internal/recovery standards to the sample prior to analysis. These standards need to replicate the behaviour of target analytes in the analytical process, which is mainly defined by the surface properties. Moreover, they need to carry a tag that can be quantified independently of the target analyte. As inductively coupled plasma mass spectrometry is used for the identification and quantification of NMs, doping with isotopes, target analytes or with chemically related rare elements is a promising approach. We present the synthesis of a library of TiO2 NMs doped with hafnium (Hf) and zirconium (Zr) (both low in environmental abundance). Zirconia NMs doped with Hf were also synthesized to complement the library. NMs were synthesized with morphological and size properties similar to commercially available TiO2. Characterization included: transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, Brunauer–Emmett–Teller total specific surface area analysis, cryofixation scanning electron microscopy, inductively coupled plasma optical emission spectroscopy and UV–visible spectrometry. The Ti : Hf and Ti : Zr ratios were verified and calculated using Rietveld refinement. The labelled NMs can serve as internal standards to track the extraction efficiency from complex matrices, and increase method robustness and traceability of characterization/quantification.

Investigation of the Zirconium Forms in Nickel Melts Containing Exogenous Refractory Oxide Nanophases

New methods for quantifying the contents of various zirconium forms in nickel, namely, zirconium solved in metal and zirconium in the form of ZrO2, are developed using inductively coupled plasma atomic emission spectrometry. It is shown that, upon the introduction of 0.40 wt % ZrO2 nanoparticles, the Zr ratio in a melt both in solution and in the form of ZrO2 nanoparticles is 1 : 80, i.e., about 99% of Zr is in the form of ZrO2. It was found that the ratio of nanoparticles in a composite material briquette affects the processes of nanoparticle assimilation by liquid metal, and ZrO2 nanoparticles lyophobic toward nickel have a tendency for agglomeration with the formation of a high-temperature carcass.

Thermal Stability of TiZrAlN and TiZrSiN Films Formed by Reactive Magnetron Sputtering

Quaternary TiZrAlN and TiZrSiN films with Ti : Zr ratio of ~1 : 1 and different Al (or Si) content were deposited by simultaneous reactive magnetron sputtering of Ti, Zr, and Al (or Si) targets under Ar + N2 plasma discharges. The elemental composition was determined by WDS and RBS methods; the phase composition was studied by X-ray diffraction. It was found that the c-(Ti,Zr,Al)N solid solution of substitution type is the basis of the (Ti,Zr)1–xAl x N (0.06 ≤ x ≤ 0.65) system. For the (Ti,Zr)1–xSi x N system (0.13 ≤ x ≤ 0.41), a dual-phase structure composed of a nanocomposite on the basis of the c-(Ti,Zr)N solid solution and grainboundary amorphous a-SiN y phase is typical. Appearance of the second a-SiN y phase promotes an amorphization of the films. Vacuum annealing of the films investigated at temperatures up to 1000°C does not lead to decomposition of the solid solutions which constitute the films. Both rather high deposition temperature (600°C) and stoichiometric nitrogen content can be the reasons for thermal stability of the films. Annealing-induced Al depletion of c-(Ti,Zr,Al)N solid solution grains is observed in (Ti,Zr)1–xAl x N films caused by the growth of the AlN based wurtzite phase at the grain boundaries.

Effects of Zr on the amorphization of Cu-Ni-Zr alloys prepared by mechanical alloying

This work presents the effects of high energy milling with different Ni and Zr ratios on the amorphization of ternary Cu-Ni-Zr alloys (initially, Cu-43Ni-7Zr, Cu-12Ni-31Zr, Cu-33Ni-7Zr, and Cu-12Ni-23Zr; and later, Cu-23Ni-15Zr and Cu-11Ni-7Zr). Microstructure was determined using X-Ray diffraction and electron microscopy. Results were compared to thermodynamic models. In the ternary alloys under study, the lattice parameter of the Cu-Ni solid solution was generally correlated to the amounts of nickel incorporated into the Cu lattice. However, longer milling times reduced that lattice parameter and facilitated Zr insertion into the solid solution. For example, after 5 h of milling time, microstructural analysis showed the formation of a solid solution with cubic structure in Cu-43Ni-7Zr. This pattern is consistent with the presence of a lattice parameter between that of Cu and Ni (α−phase); in contrast, the Cu-33Ni-7Zr alloy showed an α-phase and another similar to Zr. Results suggest that, as the amount of nickel increases, the ability to form an amorphous phase decreases. Additionally, experimental and thermodynamic data showed a solid-solution formation stage, followed by an amorphous phase formation stage that occurred as milling time and Zr content increased.

Study of the Influence of the Dielectric Composition of Al/Ti/ZrO2:Al2O3/TiN/Si/Al Structures on the Resistive Switching Behavior for Memory Applications

Nowadays both the volatile and non-volatile memories are under a high development pressure in the current industrial context. Besides the dominant solid-state memory technologies, such as DRAM and FLASH, non-volatile resistive memories (RRAM) are considered adequate candidates to complement the memory landscape [1, 2]. In spite of the interest, no consensus has been reached yet about the selection of appropriate materials for fabrication [3, 4]. The aim of this work is to deepen in the usefulness of metal transition oxides in this field, and specifically to explore the improvements on the memory behavior of metal/ZrO2/metal structures by stabilizing the metastable phase by doping or nanolaminating the dielectric films with small and controlled amounts of Al2O3. The effect on memory window, stability and robustness, as well as the comparative small-signal response are reported in this study. ZrO2:Al2O3 films were grown on highly-doped conductive Si <100> substrates covered by 10 nm thick TiN fims by means of atomic layer deposition (ALD) at 350 ºC. The reactor was a flow-type hot-wall F120. The used precursors were AlCl3 (99%, Acros Organics), ZrCl4 (99.9%, Aldrich), and O3. For electrical measurements, Al/Ti/ZrO2:Al2O3/TiN/Si/Al capacitor stacks were fabricated. Double-layer 110 nm-Al / 50 nm-Ti top electrodes were beam evaporated. The bottom electrode was provided by evaporating 100-120 nm thick Al layer on etched Si. A similar sample based on HfO2:Al2O3 was also fabricated for comparison, at 350 ºC and by using HfCl4 (99.9%, Strem) as precursor. Films characteristics of all samples are listed in Table I. The electrical characterization consisted on recording the DC and small-signal parameters by using a Keithley 4200 semiconductor analyzer. At first, all samples showed insulating behavior, but after a forming step they behaved as memory elements, with two clearly differentiate states: high-resistance state (HRS) and low-resistance state (LRS). The forming is an initial electrical stress necessary to activate the switching property, and consists on applying a DC bias ramp from 0 to ≈ 3-4 V, with a current compliance of 10 mA. In Fig. 1(a) the forming step and subsequent very first I-V memory cycles are depicted for the ZrO2-based sample. The repetitiveness of the resistive switching is shown in Fig. 1(b), in which 20 consecutive cycles are plotted. After the forming, small-signal parameters were recorded as well. Similarly, to the current, both conductance and capacitance exhibit set and reset loops [5], as it is seen in Fig. 2. In the LRS state G y C are practically constant (ohmic behavior), whereas in the HRS state the linear voltage dependencies of G and C indicate that conduction is dominated by space charge limited conduction (SCLC). To establish the influence of dielectric composition on the resistive switching performance, a comparison of the I-V loops is shown in Fig. 3 (a). The introduction of very small amounts of Al2O3 (Al:Zr = 0.16) extends the voltage range in which the loops appear, and provides narrower windows. However, the current window can be open by increasing the Al:Zr ratio (Al:Zr = 0.30), besides the voltage span diminishes. This way the resistive switching characteristic significantly improves. On the other hand, Fig. 3(b) demonstrates that thicker dielectrics lead to narrower voltage ranges but does not open the current window; finally, samples based in HfO2 instead of ZrO2 provide much lower current values. Admittance parameters sheds more light on this issue. In fact, zero-bias admittance memory maps for different Al:Zr ratios (Fig. 4) clearly show the two different states, as well as the influence of the dielectric composition. These maps represent the conductance and capacitance values measured at 0 V as a function of the programming voltage previously applied [6]. The reading process is carried out at 0 V, so without power consumption. The memory aspect ratio can be modulated by changing the amount of Al2O3. The best power consumption behavior is achieved by samples with Al:Zr = 0.30, which has the lowest values of HRS state conductance, and also the lowest values of Vset and Vreset. [1] A. Bec et al., Appl. Phys. Lett. 77(1), 139 (2000). [2] R. Waser and M. Aono, Nature Mater. 6 (11), 833 (2007). [3] E. Gale, Semicond. Sci. Technol. 29, 104004 (2014). [4] H. Nili et al., Adv. Funct. Mater. 24, 6741 (2014) [5] S. Dueñas et al. Mic. Eng. 178, 30 (2017) [6] S. Dueñas et al. EDL 38(9), 1216 (2017) Figure 1

Atomic layer deposition of PbTiO3 and PbZrxTi1-xO3 films using metal alkyl and alkylamide precursors

Atomic layer deposition (ALD) processes were demonstrated for lead-titanate (PbTiO3) and lead-zirconium-titanate (PZT) films. The metal organic precursors were tetraethyl lead Pb(Et)4 reacted with ozone; along with tetrakis ethylmethylamino zirconium and tetrakis dimethylamino titanium reacted with either water or ozone. These precursors were selected based on compatibility with ALD processes for the component oxides. Single oxide films of PbO, ZrO2, and TiO2 were easily deposited using the selected precursors. ALD of the complex oxide films was done by combining the ALD processes for the component oxide films. The compositions of Pb, Zr, and Ti in the films could be predictably controlled by the relative ratio of Pb, Zr, and Ti precursor doses during the ALD process, and controlled composition for both PbTiO3 and PZT films was demonstrated.

Vanadium Supported on Alumina and/or Zirconia Catalysts for the Selective Transformation of Ethane and Methanol

Vanadium supported on pure (Al2O3, ZrO2) or mixed zirconia-alumina (with Al/(Al + Zr) ratio of 0.75 or 0.25) catalysts have been prepared by wet impregnation, using homemade prepared supports. The catalysts have been characterized and tested in the oxidative dehydrogenation (ODH) of ethane and in the methanol aerobic transformation. The catalytic performance strongly depends on the nature of the metal oxide support. Thus, activity decreases in the order: VOx/ZrO2 &gt; VOx/(Al,Zr-oxides) &gt; VOx/Al2O3. On the other hand, at low and medium ethane conversions, the selectivity to ethylene presents an opposite trend: VOx/Al2O3 &gt; VOx/(Al,Zr-oxides) &gt; VOx/ZrO2. The different selectivity to ethylene at high conversion is due to the lower/higher initial ethylene formation and to the extent of the ethylene decomposition. Interestingly, VOx/(Al,Zr-oxides) with low Zr-loading present the lowest ethylene decomposition. The catalytic results obtained mainly depend on the nature of the supports whereas the role of the dispersion of vanadium species is unclear. In methanol oxidation, the catalysts tested present similar catalytic activity regardless of the support (Al2O3, ZrO2 or mixed Al2O3-ZrO2) but strong differences in the selectivity to the reaction products. Thus, dimethyl ether was mainly observed on alumina-supported vanadium oxide catalysts (which is associated to the presence of acidic sites on the surface of the catalyst, as determined by TPD-NH3). Formaldehyde was the main reaction product on catalysts supported on Zr-containing oxides (which can be related to a low presence of acid sites). In this article, the importance of the presence of acid sites in ethane ODH, which can be estimated using the methanol transformation reaction, is also discussed.

Acidity of co-precipitated SiO2-ZrO2 mixed oxides in the acid-catalyzed dehydrations of iso-propanol and formic acid

SiO2-ZrO2 is an interesting class of binary mixed oxide systems, but its acidity has not been intensively linked to the catalytic activity in the dehydration reactions. Thus, SiO2-ZrO2 mixed oxides with the Si/(Si + Zr) ratio ranging from 0 to 1 were synthesized via a coprecipitation method and their physicochemical properties including acid characteristics were investigated. As a result of pyridine adsorbed FT-IR and iso-propanol (IPA)-TPD, the type, quantity, concentration, and strength of acid site were largely dependent on the molar composition of SiO2-ZrO2 mixed oxides, where they reached maximum at the Si/(Si + Zr) molar ratio of 0.7. Furthermore, it was found that the catalytic activity was proportional to the acid strength in the decomposition of IPA, while the quantity of Brønsted acid sites was a principal contributor to the activity in the decomposition of formic acid.

Experimental investigation of phase equilibria in the Ti-Fe-Zr system

The phase relations of the Ti-Fe-Zr system at 873 and 1173 K were experimentally investigated by using the equilibrated alloys. Four ternary phases were determined stable at 1173 K. Two of them were line compounds with fixed Fe/(Ti, Zr) ratio, while the other two showed ellipse-shaped homogeneity. There were eight three-phase equilibria and a continuous single phase field of β(Ti, Zr) in the isothermal section at 1173 K. The solubility of Zr in Fe2(Ti, Zr) and Ti in (Fe, Ti)2Zr was measured to be 25.5 at% and 6.1 at%, respectively. The remaining binary intermetallic phases hardly dissolved the third component. The phase relationships in the isothermal section at 873 K were similar to those at 1173 K over the composition range of 0–50 at% Fe. In this isothermal section, five three-phase equilibria were observed and they were all related with the newly found ternary phases. The phase relations measured in this work are of significant difference from the existing ones obtained with the diffusion couple.

Development of High Strength Ni–Cu–Zr–Ti–Si–Sn In-Situ Bulk Metallic Glass Composites Reinforced by Hard B2 Phase

In the present study, the influence of atomic ratio of Zr to Ti on the microstructure and mechanical properties of Ni–Cu–Zr–Ti–Si–Sn alloys is investigated. The alloys were designed by fine replacement of Ti for Zr from Ni39Cu20Zr36−xTixSi2Sn3. The increase of Ti content enhances glass forming ability of the alloy by suppression of formation of (Ni, Cu)10(Zr, Ti)7 phase during solidification. With further increasing Ti content up to 24 at.%, the B2 phase is introduced in the amorphous matrix with a small amount of B19′ phase from alloy melt. The bulk metallic glass composite containing B2 phase with a volume fraction of ~ 10 vol% exhibits higher fracture strength (~ 2.5 GPa) than that of monolithic bulk metallic glass (~ 2.3 GPa). This improvement is associated to the individual mechanical characteristics of the B2 phase and amorphous matrix. The B2 phase exhibits higher hardness and modulus than those of amorphous matrix as well as effective stress accommodation up to the higher stress level than the yield strength of amorphous matrix. The large stress accommodation capacity of the hard B2 phase plays an important factor to improve the mechanical properties of in situ Ni-based bulk metallic glass composites.