Browsing by Author "Cao, P"
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- Item“114”-Type nitrides LnAl(Si4−xAlx)N7Oδ with unusual [AlN6] octahedral coordination(Wiley, 2017-02-28) Huang, S; Huang, Z; Cao, P; Zujovic, Z; Price, JR; Avdeev, M; Que, M; Suzuki, F; Kido, T; Ouyang, X; Kaji, H; Fang, M; Liu, YG; Gao, W; Söhnel, TAluminum–nitrogen six-fold octahedral coordination, [AlN6], is unusual and has only been seen in the high-pressure rocksalt-type aluminum nitride or some complex compounds. Herein we report novel nitrides LnAl(Si4−xAlx)N7Oδ (Ln=La, Sm), the first inorganic compounds with [AlN6] coordination prepared via non-high-pressure synthesis. Structure refinements of neutron powder diffraction and single-crystal X-ray diffraction data show that these compounds crystallize in the hexagonal Swedenborgite structure type with P63mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagomé layers of [SiN4] tetrahedra. Solid-state NMR data of high-purity La-114 powders confirm the unusual [AlN6] coordination. These compounds are the first examples of the “33-114” sub-type in the “114” family. The additional site for over-stoichiometric oxygen in the structure of 114-type compounds was also identified. © 1999-2021 John Wiley & Sons, Inc.
- ItemIn situ neutron diffraction observations of Ti-TiB composites(Elsevier, 2019-09) Singh, H; Hayat, M; He, Z; Peterson, VK; Das, R; Cao, PThis paper characterizes and evaluates TiB/Ti composites during thermal treatment using in situ neutron diffraction. The composites were developed using a conventional press and sinter technique. Pure titanium (Ti) was chosen as the matrix, and different concentrations of TiB2 were used as the boron source for the in situ development of the TiB phase. The conversion of phases from TiB2 (2–10 wt.%) to TiB during heating and cooling in the Ti matrix was studied for the first time using in situ neutron diffraction. No metastable phases were observed during heat-treating of the samples. Microstructural evolution and tensile properties of these composites were also evaluated with the highest tensile strength recorded of 684.95 MPa for the sample containing 5 wt.% TiB2. © 2019 Elsevier Ltd
- ItemIn situ observation and neutron diffraction of NiTi powder sintering(Elsevier, 2014-04-01) Chen, G; Liss, KD; Cao, PThis study investigated NiTi powder sintering behaviour from elemental powder mixtures of Ni/Ti and Ni/TiH2 using in situ neutron diffraction and in situ scanning electron microscopy. The sintered porous alloys have open porosities ranging from 2.7% to 36.0%. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification yet higher chemical homogenization only after high-temperature sintering. For the first time, direct evidence of the eutectoid phase transformation of NiTi at 620 °C is reported by in situ neutron diffraction. A comparative study of cyclic stress–strain behaviours of the porous NiTi alloys made from Ni/Ti and Ni/TiH2 compacts indicate that the samples sintered from the Ni/TiH2 compact exhibited a much higher porosity, larger pore size, lower fracture strength, lower close-to-overall porosity ratio and lower Young’s modulus. Instead of enhanced densification by the use of TiH2 as reported in the literature, this study shows an adverse effect of TiH2 on powder densification in NiTi.© 2013 Acta Materialia Inc.
- ItemAn in situ study of NiTi powder sintering using neutron diffraction(Multidisciplinary Digital Publishing Institute, 2015-04-03) Chen, G; Liss, KD; Cao, PThis study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2) by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of 1373 K. The phase evolution was performed by in situ neutron diffraction upon sintering and cooling. The predominant phase identified in all the produced porous NiTi alloys after being sintered at 1373 K is B2 NiTi phase with the presence of other minor phases. It is found that dehydrogenation of TiH2 significantly affects the sintering behavior and resultant microstructure. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification, yet higher chemical homogenization, after high temperature sintering but not in the case of low temperature sintering. Moreover, there is a direct evidence of the eutectoid decomposition of NiTi at ca. 847 and 823 K for Ni/Ti and Ni/TiH2, respectively, during furnace cooling. The static and cyclic stress-strain behaviors of the porous NiTi alloys made from the Ni/Ti and Ni/TiH2 compacts were also investigated. As compared with the Ni/Ti sintered samples, the samplessintered from the Ni/TiH2 compact exhibited a much higher porosity, a higher close-to-total porosity, a larger pore size and lower tensile and compressive fracture strength. © 1996-2020 MDPI
- ItemAn in situ study of sintering behavior and phase transformation Kinetics in NiTi using neutron diffraction(Springer, 2015-09-15) Chen, G; Liss, KD; Cao, PThe powder sintering behavior of NiTi from an elemental powder mixture of Ni/Ti has been investigated, using an in situ neutron diffraction technique. In the sintered alloys, the overall porosity ranges from 9.2 to 15.6 pct, while the open-to-overall porosity ratio is between 8.3 and 63.7 pct and largely depends on the sintering temperature. In comparison to powder compacts sintered at 1223 K and 1373 K (950 °C and 1100 °C), the powder compact sintered at 1153 K (880 °C) shows a much smaller pore size, a higher open-to-overall porosity ratio but smaller shrinkage and a lower density. Direct evidence of eutectoid transformation in the binary Ni-Ti system during furnace cooling to ca. 890 K (617 °C) is provided by in situ neutron diffraction. The intensities of the B2-NiTi reflections decrease during the holding stage at 1373 K (1100 °C), which has been elaborated as an extinction effect according to the dynamical theory of neutron diffraction, when distorted crystallites gradually recover to perfect crystals. The analysis on the first five reflections clarifies the non-existence of any order–disorder transition in the NiTi phase from B2-to-BCC structure.Copyright © 2015, Springer Nature
- Item(Mg,Mn,Fe,Co,Ni)O: a rocksalt high-entropy oxide containing divalent Mn and Fe(American Association for the Advancement of Science, 2023-09-20) Pu, Y; Moseley, D; He, Z; Pitike, KC; Manley, ME; Yan, J; Cooper, VR; Mitchell, VD; Peterson, VK; Johannessen, B; Hermann, RP; Cao, PHigh-entropy oxides (HEOs) have aroused growing interest due to fundamental questions relating to their structure formation, phase stability, and the interplay between configurational disorder and physical and chemical properties. Introducing Fe(II) and Mn(II) into a rocksalt HEO is considered challenging, as theoretical analysis suggests that they are unstable in this structure under ambient conditions. Here, we develop a bottom-up method for synthesizing Mn- and Fe-containing rocksalt HEO (FeO-HEO). We present a comprehensive investigation of its crystal structure and the random cation-site occupancy. We show the improved structural robustness of this FeO-HEO and verify the viability of an oxygen sublattice as a buffer layer. Compositional analysis reveals the valence and spin state of the iron species. We further report the antiferromagnetic order of this FeO-HEO below the transition temperature ~218 K and predict the conditions of phase stability of Mn- and Fe-containing HEOs. Our results provide fresh insights into the design and property tailoring of emerging classes of HEOs. © 2024 American Association for the Advancement of Science.
- ItemUsing neutron diffraction to explore lithium displacement within cubic phase stabilised Ga-doped Li6.75La3Zr1.75Ta0.25O12 lithium garnet oxides(Elsevier, 2023-12-15) Christopher, TD; Zhang, T; Huang, S; Zujovic, Z; Avdeev, M; Cao, P; Söhnel, TTypical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75–3xGaxLa3Zr1.75Ta0.25O12 x ≥ 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY licence.