Browsing by Author "Cai, Z"

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    The complementarity of PIXE and synchrotron induced X-ray methods for the characterisation of combustion sources contributing to urban air pollution
    (Elsevier, 2002-04) Cohen, DD; Siegele, R; Stelcer, E; Garton, DB; Stampfl, APJ; Cai, Z; Ilinski, P; Rodrigues, W; Legnini, DG; Yun, W; Lai, B
    Current knowledge of fine-particle airborne pollution concentrations and constituents with diameters below 2.5 μm (PM2.5) is limited. Sources are both natural and man-made. Here we describe two types of experiments performed using the advanced photon source facility at Chicago, and compare the results with PIXE analysis on the same fine particle filters. These are firstly broad beam (2 mm) studies with tuned synchrotron beam energies to help resolve over-lapping X-rays, and secondly highly focused X-ray beam studies (0.2 μm) of individual fine particles from airborne pollution combustion sources. © 2002 Elsevier Science B.V.
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    Disorder-induced spin-liquid-like behavior in kagome-lattice compounds
    (American Physical Society (APS), 2020-12-15) Ma, Z; Dong, ZY; Wu, S; Zhu, Y; Bao, S; Cai, Z; Wang, W; Shangguan, Y; Wang, J; Ran, K; Yu, DH; Deng, GC; Mole, RA; Li, HF; Yu, SL; Li, JX; Wen, JS
    Quantum spin liquids (QSLs) are an exotic state of matter that is subject to extensive research. However, the relationship between the ubiquitous disorder and the QSL behaviors is still unclear. Here, by performing comparative experimental studies on two kagomé-lattice QSL candidates, Tm3Sb3Zn2O14 and Tm3Sb3Mg2O14, which are isostructural to each other but with strong and weak structural disorder, respectively, we show unambiguously that the disorder can induce spin-liquid-like features. In particular, both compounds show dominant antiferromagnetic interactions with a Curie-Weiss temperature of -17.4 and -28.7 K for Tm3Sb3Zn2O14 and Tm3Sb3Mg2O14, respectively, but remain disordered down to about 0.05 K. Specific-heat results suggest the presence of gapless magnetic excitations characterized by a residual linear term. Magnetic excitation spectra obtained by inelastic neutron scattering (INS) at low temperatures display broad continua. All these observations are consistent with those of a QSL. However, we find in Tm3Sb3Zn2O14, which has strong disorder resulting from the random mixing of the magnetic Tm3+ and nonmagnetic Zn2+, that the low-energy magnetic excitations observed in the specific-heat and INS measurements are substantially enhanced compared to those of Tm3Sb3Mg2O14, which has much less disorder. We believe that the effective spins of the Tm3+ ions in the Zn2+/Mg2+ sites give rise to the low-energy magnetic excitations, and the amount of the occupancy determines the excitation strength. These results provide direct evidence of the mimicry of a QSL caused by disorder. ©2020 American Physical Society.
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    Fe Site order and magnetic properties of Fe1/4NbS2
    (American Chemical Society (ACS), 2023-11-06) Lawrence, EA; Huai, XD; Kim, DW; Avdeev, M; Chen, Y; Skorupskii, G; Miura, A; Ferrenti, A; Waibel, M; Kawaguchi, S; Ng, N; Kaman, B; Cai, Z; Schoop, L; Kushwaha, S; Liu, F; Tran, TT; Ji, H
    Transition-metal dichalcogenides (TMDs) have long been attractive to researchers for their diverse properties and high degree of tunability. Most recently, interest in magnetically intercalated TMDs has resurged due to their potential applications in spintronic devices. While certain compositions featuring the absence of inversion symmetry such as Fe1/3NbS2 and Cr1/3NbS2 have garnered the most attention, the diverse compositional space afforded through the host matrix composition as well as intercalant identity and concentration is large and remains relatively underexplored. Here, we report the magnetic ground state of Fe1/4NbS2 that was determined from low-temperature neutron powder diffraction as an A-type antiferromagnet. Despite the presence of overall inversion symmetry, the pristine compound manifests spin polarization induced by the antiferromagnetic order at generic k points, based on density functional theory band-structure calculations. Furthermore, by combining synchrotron diffraction, pair distribution function, and magnetic susceptibility measurements, we find that the magnetic properties of Fe1/4NbS2 are sensitive to the Fe site order, which can be tuned via electrochemical lithiation and thermal history. © 2023 American Chemical Society.
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    Reversible electrochemical lithium cycling in a vanadium(IV)- andnNiobium(V)-based Wadsley–Roth phase
    (American Chemical Society (ACS), 2023-05-09) Lawrence, EA; Davenport, MA; Devi, R; Cai, Z; Avdeev, M; Belnap, JR; Liu, J; Alnaser, H; Ho, A; Sparks, TD; Gautam, GS; Allred, JM; Ji, HW
    Fast charging remains one of the greatest safety challenges in Li-ion batteries due to Li-dendrite growth occurring on graphite anodes if they are lithiated too quickly. The search for high-rate anodes has highlighted materials in the Wadsley-Roth (WR) shear phase family. The relative abundance of V compared with traditional WR compositions of Nb and W makes V-based phases attractive. However, the high voltage and poor reversibility typically associated with V redox have made V-rich WR phases less studied than Nb- and W-rich phases. Here, we show that a new V-rich Wadsley-Roth phase, V7Nb6O29, achieves excellent rate capability and 80% capacity retention after 228 cycles with a relatively low average voltage of 1.76 V vs Li/Li+ compared with other V-rich WR phases. Single-crystal X-ray diffraction reveals a P4/m space group with repeating 2 × 2 × ∞ and 3 × 3 × ∞ blocks of V4+ and Nb5+ octahedra. Combined neutron pair distribution function analysis, X-ray absorption spectroscopy, and density functional theory calculations show that V redox is the primary source of capacity and that cycling stability is provided by the stable octahedral coordination adopted by V4+ in the material. © American Chemical Society