Gordon J. Miller

Bio: Gordon J. Miller is an academic researcher from Iowa State University. The author has contributed to research in topics: Intermetallic & Crystal structure. The author has an hindex of 35, co-authored 301 publications receiving 5992 citations. Previous affiliations of Gordon J. Miller include Max Planck Society & RWTH Aachen University.

Structural-electronic relationships in inorganic solids: powder neutron diffraction studies of the rutile and anatase polymorphs of titanium dioxide at 15 and 295 K

Abstract: Rietveld analysis of time-of-flight pulsed neutron diffraction of powders shows a nearly isotropic shrinkage of the structures of both the rutile and anatase polymorphs of TiO/sub 2/ upon cooling from 295 to 15 K and no change in the sense of the distortion of the TiO/sub 6/ octahedra (two long and four short Ti-O distances in both): rutile at 295 (first) and 15 K (second), a/sub 0/ 4.593 08 (4), 4.586 66 (4), c/sub 0/, 2.958 89 (3), 2.954 07 (3), x/sub oxygen/, 0.304 76 (6), 0.304 69 (6), Ti-O(4x), 1.9486 (3), 1.9459 (3), Ti-O(2X), 1.9796 (4), 1.9764 (4); anatase at 295 and 15 K, a/sub 0/, 3.784 79 (3), c/sub 0/, 9.502 26 (12), 0.504 65 (12), x/sub oxygen/, 0.16686 (5), 0.166 75 (4), Ti-O(4x), 1.9338 (1), 1.9322 (1), Ti-O(2X), 1.9799 (5), 1.9788 (4): all distances (A) referenced to silicon (a = 5.430 88 A). Both tight-binding calculations on the crystalline solids and molecular mechanics computations on the oxide lattice alone lead to a model in which the balance of attractive Ti-O and repulsive O-O interactions control the details of the overall structures. The relative bond lengths around metal centers in some other systems are predicted.

Making and breaking covalent bonds across the magnetic transition in the giant magnetocaloric material Gd5(Si2Ge2)

Abstract: A temperature-dependent, single crystal x-ray diffraction study of the giant magnetocaloric material, ${\mathrm{Gd}}_{5}({\mathrm{Si}}_{2}{\mathrm{Ge}}_{2})$, across its Curie temperature (276 K) reveals that the simultaneous orthorhombic to monoclinic transition occurs by a shear mechanism in which the $(\mathrm{Si},\mathrm{Ge})\ensuremath{-}(\mathrm{Si},\mathrm{Ge})$ dimers that are richer in Ge increase their distances by 0.859(3) \AA{} and lead to twinning. The structural transition changes the electronic structure, and provides an atomic-level model for the change in magnetic behavior with temperature in the ${\mathrm{Gd}}_{5}({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{)}_{4}$.

Anisotropy and large magnetoresistance in the narrow-gap semiconductor FeSb2

Abstract: A study of the anisotropy in magnetic, transport, and magnetotransport properties of ${\mathrm{FeSb}}_{2}$ has been made on large single crystals grown from Sb flux. Magnetic susceptibility of ${\mathrm{FeSb}}_{2}$ shows diamagnetic to paramagnetic crossover around 100 K. Electrical transport along two axes is semiconducting, whereas the third axis exhibits a metal-semiconductor crossover at temperature ${T}_{\mathrm{cr}}$ which is sensitive to current alignment and ranges between 40 and 80 K. In $H=70\mathrm{kOe}$ semiconducting transport is restored for $Tl300\mathrm{K},$ resulting in large magnetoresistance $[\ensuremath{\rho}(70\mathrm{kOe})\ensuremath{-}\ensuremath{\rho}(0)]/\ensuremath{\rho}(0)=2200%$ in the crossover temperature range.

Magnetic field effects on transport properties of PtSn4

Abstract: The anisotropic physical properties of single crystals of orthorhombic PtSn${}_{4}$ are reported for magnetic fields up to 140 kOe, applied parallel and perpendicular to the crystallographic b axis. The magnetic susceptibility has an approximately temperature-independent behavior and reveals an anisotropy between the ac plane and b axis. Clear de Haas-van Alphen oscillations in fields as low as 5 kOe and at temperatures as high as 30 K were detected in magnetization isotherms. The thermoelectric power and resistivity of PtSn${}_{4}$ show the strong temperature and magnetic field dependencies. A change of the thermoelectric power at $H=140$ kOe is observed as high as $\ensuremath{\simeq}$50 $\ensuremath{\mu}$V/K. Single crystals of PtSn${}_{4}$ exhibit very large transverse magnetoresistance of $\ensuremath{\simeq}$$5\ifmmode\times\else\texttimes\fi{}{10}^{5}$% for the ac plane and of $\ensuremath{\simeq}$$1.4\ifmmode\times\else\texttimes\fi{}{10}^{5}$% for the b axis resistivity at 1.8 K and 140 kOe, as well as pronounced Shubnikov de Haas oscillations. The magnetoresistance of PtSn${}_{4}$ appears to obey Kohler's rule in the temperature and field range measured. The Hall resistivity shows a linear temperature dependence at high temperatures followed by a sign reversal around 25 K which is consistent with thermoelectric power measurements. The observed quantum oscillations and band structure calculations indicate that PtSn${}_{4}$ has three-dimensional Fermi surfaces.

Anatase TiO(2) single crystals with a large percentage of reactive facets

Abstract: [Yang, Hua Gui; Sun, Cheng Hua; Qiao, Shi Zhang; Liu, Gang; Smith, Sean Campbell; Lu, Gao Qing] Univ Queensland, ARC Ctr Excellence Funct Nanomat, Sch Engn, Brisbane, Qld 4072, Australia. [Yang, Hua Gui; Sun, Cheng Hua; Qiao, Shi Zhang; Liu, Gang; Smith, Sean Campbell; Lu, Gao Qing] Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Computat Mol Sci, Brisbane, Qld 4072, Australia. [Zou, Jin] Univ Queensland, Ctr Microscopy & Microanal, Brisbane, Qld 4072, Australia. [Zou, Jin] Univ Queensland, Sch Engn, Brisbane, Qld 4072, Australia. [Liu, Gang; Cheng, Hui Ming] Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat sci, Shenyang 110016, Peoples R China.;Lu, GQ (reprint author), Univ Queensland, ARC Ctr Excellence Funct Nanomat, Sch Engn, Brisbane, Qld 4072, Australia;s.qiao@uq.edu.au maxlu@uq.edu.au

Recent developments in magnetocaloric materials

Abstract: The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM2, where M = Al, Co and Ni), Gd5(Si1−xGex)4 ,M n(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) and their hydrides and the manganites (R1−xMxMnO3, where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material. (Some figures in this article are in colour only in the electronic version)

Graphene/Polymer Nanocomposites

Abstract: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives f...

Review of the anatase to rutile phase transformation

Abstract: Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

Transition-metal-based magnetic refrigerants for room-temperature applications

Abstract: Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration1. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.