Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XVI: Phase Stability & Phase Equilibria
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Shih-kang Lin, National Cheng Kung University; Chao-hong Wang, National Chung Cheng University; Jae-Ho Lee, Hongik University; Ikuo Ohnuma, National Institute for Materials Science (NIMS); Chih-Ming Chen, National Chung Hsing University; Thomas Reichmann, Karlsruhe Institute of Technology; Yu Zhong, Florida International University; Shijo Nagao, Osaka University; Shien Ping Tony Feng, The University of Hong Kong; Yee-wen Yen, National Taiwan Univ of Science & Tech

Monday 2:00 PM
February 27, 2017
Room: 25A
Location: San Diego Convention Ctr

Session Chair: Shih-kang Lin, National Cheng Kung University; Chih-Ming Chen, National Chung Hsing University

2:00 PM  Invited
Zirconia Mystery? Why and How Zirconia Phases and Phase Diagrams Have Been Misunderstood for a Long Time?: Masahiro Yoshimura1; 1NatIonal Cheng Kung University
    Confusions and misunderstands have come from metastable phases. Zirconia(ZrO2) and its solid solutions have three modifications:Cubic(c),Tetragonal(t),and Monoclinic(m) ones. In addition to them they can also form various metastable phases:c’(=t’’),t’ and m’ with the same symmetry of c,t and m. Our >30 years' studies have established many phase diagrams including those stable and metastable phases for various ZrO2-R2O3(R=rare earths),ZrO2-CeO2 as well as some HfO2 systems. The metastable phases would be formed by some reasons,[1] Diffusion-less phase transformations: c-c’(=t’’),t-t’,m-m’ and t’’-t’ occur immediately. They are generally reversible due to diffusion-less nature except for t’’-t’. [2]Diffusional phase transformations and/or phase changes: c - c+t,t -m+c require a long time heating and annealing because they need compositional changes due to slow cation diffusions. It is very slow ca. 105 times slower than anion diffusion. [3] “Frozen” phase boundaries with wide solubilities would occur at low temperatures particularly below 1000 C in reported diagrams.

2:30 PM  
Searching for New Permanent Magnetic Phases: The Systems Bi-Mn-T (T = Ni, Rh, Pt): Peter Kainzbauer1; Martin Marker1; Klaus Richter1; Herbert Ipser1; 1University of Vienna
    It is well known that the intermetallic compound α-BiMn possesses highly interesting magnetic properties. However, due to its peritectic formation at a low temperature (355C) it is virtually impossible to prepare phase-pure bulk BiMn. Therefore, the search has been extended into different ternary systems, among them Bi-Mn-Ni, Bi-Mn-Rh, and Bi-Mn-Pt. Phase equilibria in these three ternary systems were studied by standard experimental methods as DTA, XRD, SEM and EPMA. The results will be presented as isothermal sections at different temperatures, different isopleths and (partial) liquidus projections.

2:50 PM  
Phase Stability of Mixed-Cation Alkaline-Earth Hexaborides: Insights from X-ray Diffraction and High-resolution Transmission Electron Microscopy: James Cahill1; Michael Alberga2; Doreen Edwards2; Scott Misture2; Victor Vasquez3; Olivia Graeve1; 1University of California, San Diego; 2Alfred University; 3University of Nevada, Reno
    The phase stability of mixed-cation alkaline-earth hexaborides is studied. These materials have the potential for use as hydrogen storage sources. The results show separation of the MB6 phase into multiple solid solutions with varying compositions in ternary (Ba-Ca)B6 and (Ba-Sr)B6 powders. X-ray diffraction data contains peak splitting and asymmetry and high-resolution transmission electron microscopy confirms the presence of these phases in the form of homogenous nano-regimes in individual equilibrium. Thermal treatments ranging from 1000-1700C enhance the overall homogeneity of the samples and merge the phases into one, indicating that the as-synthesized state is thermodynamically unstable as the collection of nano-regimes results in increased microstrain and lattice imperfections. Analysis of the chemical reactions that occur during synthesis suggests that the decomposition of the metal precursors (nitrates and carbonates) to metal oxides introduces variance into the formation process of mixed-cation hexaboride compounds, producing nano-regimes within the crystal lattice.

3:10 PM  
Effect of Structural Order on Pulsed Laser Crystallization Kinetics of Amorphous Germanium Thin Films: Tian Li1; Leonardus Bimo Bayu Aji1; Tae Wook Heo1; Melissa Santala2; Sergei Kucheyev1; Geoffrey Campbell1; 1Lawrence Livermore National Laboratory; 2Oregon State University
    The structural-property relationship during pulsed laser crystallization of amorphous Ge (a-Ge) thin film was investigated using in-situ TEM measurements coupled with phase-field modeling. Sputter deposited a-Ge had its nanostructure altered by irradiation with high-energy Ar+ ions. The change in structure resulted in a reduction in medium range order (MRO) characterized using fluctuation electron microscopy. The pulsed laser crystallization kinetics of the as-deposited versus irradiated materials were measured using the dynamic transmission electron microscope (DTEM) operated in the multi-frame movie mode. The propagation rate of the crystallization front for the irradiated material was lower; the changes were correlated to the MRO difference and formation of a thin liquid layer during crystallization as suggested by phase-field modeling results. This work performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under SCW0974 by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

3:30 PM Break

3:50 PM  
In-situ Characterization of the Transverse Propagation Mechanism for Crystallization of Amorphous Germanium and the Resulting Microstructure: Garth Egan1; Tian Li1; John Roehling1; Joseph Mckeown1; Geoffrey Campbell1; 1Lawrence Livermore National Laboratory
    Semiconductor thin films are often deposited amorphous and processed using laser induced crystallization for applications such as solar cells, IR detectors, and digital displays. Under certain conditions, germanium will crystallize in discrete bands that propagate transverse to the direction of net crystallization. These kinetics were studied using our Dynamic Transmission Electron Microscope (DTEM) in Movie Mode. This enabled direct observation of the crystallization front with submicron spatial resolution as it propagated at rates up to 10 m/s. The resultant anisotropic microstructure was further explored using orientation mapping. This paper will present these results along with our hypothesis for a mechanism involving liquid mediated crystal growth enabled as the local amorphous region reaches a critical temperature. This work was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering for FWP SCW0974 by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

4:10 PM  
High Temperature Phase Stability of α2-Cu3Al in Binary Cu-Al Alloys: Issues in the Al-Cu Phase Diagram: Valery Ouvarov-Bancalero1; Choong-Un Kim1; 1The University of Texas at Arlington
    This research reports experimental observations concluding that the thermal stability of the α2-Cu3Al intermetallic compound in the Cu-Al binary system goes way beyond its peritectoid decomposition at 363°C, suggesting that the currently accepted Cu-Al phase diagram may contain errors in representing phase equilibria at the Cu-rich end. This conclusion is evidenced by an interdiffusion study conducted with diffusion couples of thick Cu plates coated with 2μm thick Al thin films. X-ray diffraction coupled with Rietveld refinement, and electron microscope characterizations carried out after annealing between 450 and 750°C, yield irrevocable evidence supporting the existence of α2-Cu3Al at high temperatures. It is further found that α2-Cu3Al coexist with the equilibrium phase β above 650°C on the Cu side of the diffusion couple. These results along with discussions as to their implications to the phase equilibria in Al-Cu binary system and reinterpretation of results in similar investigation to ours will be presented.

4:30 PM  
Thermodynamic Study on PMN-PT Single Crystals: Hooman Sabarou1; Yu Zhong1; 1Florida International University
    A new thermodynamic approach on the structural evolution of Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal has been presented, and it is used to justify the inconsistency of the ferroelectric properties of single-crystal perovskite. A series of experimental tests under different temperatures and oxygen partial pressures has been applied to simulate the required working conditions of these materials. The phase stability and structural changes have been scrutinized via X-ray diffraction and thermogravimetric methods. The involved mechanisms for crystal symmetry changes and stabilizing perovskite structure clearly explain the degradation of the piezoelectric properties of the single crystals and competently match with their electric polarization measurements. The thermodynamic approach discusses the origin of the polarization hysteresis degradation and provides conditions to save ferroelectric properties.