Halasyamani, P. Shiv - University of Houston

个人简介

Postdoctoral Fellow, Oxford University, 1997-1998 Ph.D., Northwestern University, 1996 B.S., University of Chicago, 1992

研究领域

Research in the Halasyamani group involves the synthesis, characterization, and development of structure-property relationships in new functional inorganic materials. Functionalities we are interested in include second-order non-linear optical behavior, i.e. second-harmonic generation, piezoelectricity, ferroelectricity, pyroelectricity, and multi-ferroic behavior. In addition to bulk phase synthesis, we also have research programs in large single crystal growth. We utilize a range of diffraction (powder and single crystal X-ray) and non-diffraction (TG/DSC, powder SHG, pyroelectric, etc.) measurements to characterize the materials. Specific research areas include - A broad area that we are investigating involves the synthesis, characterization, and structure-property relationships in new polar oxides. Polar materials, those that exhibit a macroscopic dipole moment, exhibit a host of technologically important properties including piezoelectricity, ferroelectricity, and pyroelectricity. We have demonstrated that the incidence of polarity in any new oxide material can be increased by incorporating second-order Jahn-Teller (SOJT) disorted cations. With respect to crystal chemistry, SOJT distortions are observed in oxide environments of octahedrally coordinated d0 transition metals, e.g. Ti4+, Nb5+, and W6+ and cations with non-bonded electron pairs, e.g. Sn2+, Sb3+, and Te4+. We have exploited this distortion and have successfully synthesized a variety of polar materials. We characterize the materials through second-order non-linear optical, i.e. SHG, measurements as well as piezoelectric and polarization measurements. Our recent work has incorporated theoretical calculations to better understand the energetic of polarization reversal. Another area of research we are investigating involves large single crystal growth – crystals centimeter size or larger. Large single crystals are crucial for detailed physical property measurements that can provide a far better understanding of structure-property relationships. We use a top-seeded solution growth (tssg) technique to grow centimeter size crystals of our functional materials. Currently, we have eight (8) tssg crystal growth furnaces with a maximum temperature of 1200C. This technique has enabled us to grow large crystals of a variety of materials including Na2TeW2O9 and LiFeP2O7 (see Figures above – left and right respectively). An additional area of research we are involved with concerns multi-ferroic fluorides. For our purposes, multi-ferroic materials exhibit ferroelectricity, i.e. reversible polarization, and some sort of magnetic ordering. We are investigating magnetic ordering in materials that undergo a ‘non-classic’ ferroelectric mechanism, e.g., BaNiF4 (see Figure). As seen in the Figure, the green octahedra and yellow spheres represent the structure of the ‘up’ polarization of BaNiF4, whereas the gray octahedral and spheres represent the structure of the ‘down’ polarization. The structural re-orientation through the NiF6 octahedral rotations and Ba2+ displacements result in the polarization reversal, switching between ‘up’ and ‘down’, i.e. the ferroelectric behavior. We are investigating a host of mixed-metal fluorides that could undergo this non-classic ferroelectric mechanism and exhibit magnetic ordering.

近期论文

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Donakowski, M.D., Gautier, R., Lu, H., Tran, T.T., Cantwell, J., Halasyamani, P.S., and Poeppelmeier, K.R., Synthesis of Two Vanadium Oxide-Fluoride Materials that Differ in Phase Matchability, Inorg. Chem., Submitted, 2014. Patino, M.A., Smith, M., Zhang, W., Halasyamani, P.S., and Hayward, M.A., Cation Exchange in a 3D Perovskite - Synthesis of Ni0.5TaO3, Inorg. Chem., In Press, 2014. Thao, T.T., Halasyamani, P.S., and Rondinelli, J., Role of Acentric Displacements on the Crystal Structure and Second-Harmonic Generating Properties of RbPbCO3F and CsPbCO3F, Inorg. Chem., In Press, 2014. Greenblatt, M., Retuerto, M., Li, M., Ignatov, A., Croft, M., Hodges, J., Tran, T.T. and Halasyamani, P.S., Crystallographic and magnetic properties of Pb2-xBixIr2O7-d, Mater. Res. Express, Submitted, 2014. Thao, T.T. and Halasyamani, P.S., Synthesis and Characterization of ASnF3 (A = Na+, K+, Cs+), J. Solid State Chem., 210, 213-218, 2014. Aliev, A., Endara, D., Huve, M., Colmont, M., Roussel, P., Tran, T. T., Halasyamani, P.S., and Mentre, O., Labile degree of disorder in Bismuth-oxyphosphates compounds: illustration through three new structural types, Inorg. Chem., 53, 861-871, 2014. Holland, M, Donakowski, M.D., Pozzi, E.A., Rasmussen, A.M., Tran, T.T., Pease-Dodson, S.E., Halasyamani, P.S., Seideman, T., Van Duyne, R.P., Poeppelmeier, K.R., Polar Alignment of Lambda-Shaped Basic Building Units within Transition Metal Oxide Fluoride Materials, Inorg. Chem., 53, 221-228, 2014. Luo, K., Tran, T.T., Halasyamani, P.S., and Hayward, M.A., Synthesis and Selective Topochemical Fluorination of the cation and anion-vacancy ordered phases Ba2YCoO5 and Ba3YCo2O7.5, Inorg. Chem., 52, 13762-13769, 2013. Pachoud, E., Zhang, W., Tapp, J., Liang, K.-C., Lorenz, B., Chu, C.W., and Halasyamani, P.S., Single Crystal Growth, Structure, and Physical Properties of LiCrP2O7, Cryst. Growth Des., 13, 5473-5480, 2013. Yeon, J., Smith, M.D., Sefat, A.S., Tran, T.T., Halasyamani, P.S., zur Loye, H.C., U3F12(H2O), a Non-Centrosymmetric Uranium Fluoride Prepared via a Convenient In-Situ Route that Creates of U4+ Cations under Mild Hydrothermal Conditions, Inorg. Chem., 52, 8303-8305, 2013.