Physics demos for all UVEG degrees: a unique project in Spain

The Physics Demo Project at the University of Valencia (www.uv.es/fisicademos) has developed a collection of physics demonstrations to be used during lectures. It consists of more than 130 experimental demos about different physics topics. More than 30 professors borrow them whenever they lecture on physics in any of our 40 courses in 17 different science or technical degrees, involving 246 ECTS and more than 3500 students. Each demo kit with a simple experimental set displays a particular physics phenomenon. An on-line user guide highlights the main physics principles involved, instructions on how to use it and advices of how to link it to the theoretical concepts or to technical applications. Demo lectures (and collections) are a usual and widespread practice in many countries but not in Spain. This unique initiative aims at the recovery of this practice by involving a growing collaborative team of users and with the aid of educational innovation projects. Here we explain the project content, organization and recent developments. Our experience, together with the positive students comments, allows us to draw the following conclusions: demos introduce the real sensible world in the lecture hall, providing the necessary link between concepts and everyday life, and becoming, again, something more than "chalk and talk"

Light-induced transmission nonlinearities in gallium selenide

The intensity of a He–Ne laser (633 nm, 5 mW) transmitted by different GaSe samples is observed to change in correlation with a Nd-yttrium–aluminum–garnet laser pulse (532 nm, 7.8 ns, 3 mJ) which excites them. Such time response has been attributed to a nonlinear optical effect, i.e., a decrease in the refractive index due to the exciton screening by the photogenerated carriers. A calculation of the absorption coefficient and refractive index at different carrier concentrations has led to a reconstruction of transmittance transients which fully agree with the experimental data at different incident intensities and [email protected] ; [email protected] ; [email protected] ; [email protected]

High-pressure x-ray diffraction and ab initio study of Ni2Mo3N, Pd2Mo3N, Pt2Mo3N, Co3Mo3N, and Fe3Mo3N: Two families of ultra-incompressible bimetallic interstitial nitrides

We have studied by means of high-pressure x-ray diffraction the structural stability of Ni2Mo3N, Co3Mo3N, and Fe3Mo3N. We also report ab initio computing modeling of the high-pressure properties of these compounds, Pd2Mo3N, and Pt2Mo3N. We have found that the nitrides remain stable in the ambient-pressure cubic structure at least up to 50 GPa and determined their equation of state. All of them have a bulk modulus larger than 300 GPa. Single-crystal elastic constants have been calculated in order to quantify the stiffness of the investigated nitrides. We found that they should have a Vickers hardness similar to that of cubic spinel nitrides like gamma-Si3N4Comment: 25 pages, 6 figures, 3 table

Determination of the high-pressure crystal structure of BaWO4 and PbWO4

We report the results of both angle-dispersive x-ray diffraction and x-ray absorption near-edge structure studies in BaWO4 and PbWO4 at pressures of up to 56 GPa and 24 GPa, respectively. BaWO4 is found to undergo a pressure-driven phase transition at 7.1 GPa from the tetragonal scheelite structure (which is stable under normal conditions) to the monoclinic fergusonite structure whereas the same transition takes place in PbWO4 at 9 GPa. We observe a second transition to another monoclinic structure which we identify as that of the isostructural phases BaWO4-II and PbWO4-III (space group P21/n). We have also performed ab initio total energy calculations which support the stability of this structure at high pressures in both compounds. The theoretical calculations further find that upon increase of pressure the scheelite phases become locally unstable and transform displacively into the fergusonite structure. The fergusonite structure is however metastable and can only occur if the transition to the P21/n phases were kinetically inhibited. Our experiments in BaWO4 indicate that it becomes amorphous beyond 47 GPa.Comment: 46 pages, 11 figures, 3 table

High-pressure study of the behavior of mineral barite by X-ray diffraction

In this paper, we report the angle-dispersive x-ray diffraction data of barite, BaSO 4, measured in a diamond-anvil cell up to a pressure of 48 GPa, using three different fluid pressure-transmitting media (methanol-ethanol mixture, silicone oil, and He). Our results show that BaSO 4 exhibits a phase transition at pressures that range from 15 to 27 GPa, depending on the pressure media used. This indicates that nonhydrostatic stresses have a crucial role in the high-pressure behavior of this compound. The new high-pressure (HP) phase has been solved and refined from powder data, having an orthorhombic P2 12 12 1 structure. The pressure dependence of the structural parameters of both room- and HP phases of BaSO 4 is also discussed in light of our theoretical first-principles total-energy calculations. Finally, a comparison between the different equations of state obtained in our experiments is reported. © 2011 American Physical Society.Financial support from the Spanish Consolider Ingenio 2010 Program (Project No. CDS2007-00045) is acknowledged. The work was also supported by Spanish MICCIN under Projects No. CTQ2009-14596-C02-01 and No. MAT2010-21270-C04-01 as well as from Comunidad de Madrid and European Social Fund: S2009/PPQ-1551 4161893 (QUIMAPRES). The ESRF is acknowledged for provision of beamtime.Santamaría-Pérez, D.; Gracia, L.; Garbarino, G.; Beltrán, A.; Chuliá-Jordán, R.; Gomis Hilario, O.; Errandonea, D.... (2011). High-pressure study of the behavior of mineral barite by X-ray diffraction. Physical Review B. 84:54102-1-54102-8. https://doi.org/10.1103/PhysRevB.84.054102S54102-154102-884RUBIN, A. E. (1997). Mineralogy of meteorite groups. Meteoritics & Planetary Science, 32(2), 231-247. doi:10.1111/j.1945-5100.1997.tb01262.xVegas, A. (2000). Cations in Inorganic Solids. Crystallography Reviews, 7(3), 189-283. doi:10.1080/08893110008044245Santamaría-Pérez, D., & Vegas, A. (2003). The Zintl–Klemm concept applied to cations in oxides. I. The structures of ternary aluminates. Acta Crystallographica Section B Structural Science, 59(3), 305-323. doi:10.1107/s0108768103005615Vegas, A., & Jansen, M. (2001). Structural relationships between cations and alloys; an equivalence between oxidation and pressure. Acta Crystallographica Section B Structural Science, 58(1), 38-51. doi:10.1107/s0108768101019310Lee, P.-L., Huang, E., & Yu, S.-C. (2001). Phase diagram and equations of state of BaSO4. High Pressure Research, 21(2), 67-77. doi:10.1080/08957950108201005Lee, P.-L., Huang, E., & Yu, S.-C. (2003). High-pressure Raman and X-ray studies of barite, BaSO4. High Pressure Research, 23(4), 439-450. doi:10.1080/0895795031000115439Crichton, W. A., Merlini, M., Hanfland, M., & Muller, H. (2011). The crystal structure of barite, BaSO4, at high pressure. American Mineralogist, 96(2-3), 364-367. doi:10.2138/am.2011.3656Errandonea, D., Santamaria-Perez, D., Bondarenko, T., & Khyzhun, O. (2010). New high-pressure phase of HfTiO4 and ZrTiO4 ceramics. Materials Research Bulletin, 45(11), 1732-1735. doi:10.1016/j.materresbull.2010.06.061López-Solano, J., Rodríguez-Hernández, P., Muñoz, A., Gomis, O., Santamaría-Perez, D., Errandonea, D., … Raptis, C. (2010). Theoretical and experimental study of the structural stability ofTbPO4at high pressures. Physical Review B, 81(14). doi:10.1103/physrevb.81.144126Hammersley, A. P., Svensson, S. O., Hanfland, M., Fitch, A. N., & Hausermann, D. (1996). Two-dimensional detector software: From real detector to idealised image or two-theta scan. High Pressure Research, 14(4-6), 235-248. doi:10.1080/08957959608201408Mao, H. K., Xu, J., & Bell, P. M. (1986). Calibration of the ruby pressure gauge to 800 kbar under quasi-hydrostatic conditions. Journal of Geophysical Research, 91(B5), 4673. doi:10.1029/jb091ib05p04673Rodríguez-Carvajal, J. (1993). Recent advances in magnetic structure determination by neutron powder diffraction. Physica B: Condensed Matter, 192(1-2), 55-69. doi:10.1016/0921-4526(93)90108-iBecke, A. D. (1993). Density‐functional thermochemistry. III. The role of exact exchange. The Journal of Chemical Physics, 98(7), 5648-5652. doi:10.1063/1.464913Lee, C., Yang, W., & Parr, R. G. (1988). Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Physical Review B, 37(2), 785-789. doi:10.1103/physrevb.37.785Gracia, L., Beltrán, A., & Andrés, J. (2007). Characterization of the High-Pressure Structures and Phase Transformations in SnO2. A Density Functional Theory Study. The Journal of Physical Chemistry B, 111(23), 6479-6485. doi:10.1021/jp067443vGracia, L., Beltrán, A., & Errandonea, D. (2009). Characterization of theTiSiO4structure and its pressure-induced phase transformations: Density functional theory study. Physical Review B, 80(9). doi:10.1103/physrevb.80.094105Blanco, M. A., Francisco, E., & Luaña, V. (2004). GIBBS: isothermal-isobaric thermodynamics of solids from energy curves using a quasi-harmonic Debye model. Computer Physics Communications, 158(1), 57-72. doi:10.1016/j.comphy.2003.12.001Errandonea, D., Santamaría-Perez, D., Vegas, A., Nuss, J., Jansen, M., Rodríguez-Hernandez, P., & Muñoz, A. (2008). Structural stability ofFe5Si3andNi2Sistudied by high-pressure x-ray diffraction andab initiototal-energy calculations. Physical Review B, 77(9). doi:10.1103/physrevb.77.094113Santamarı́a-Pérez, D., Nuss, J., Haines, J., Jansen, M., & Vegas, A. (2004). Iron silicides and their corresponding oxides: a high-pressure study of Fe5Si3. Solid State Sciences, 6(7), 673-678. doi:10.1016/j.solidstatesciences.2004.03.027Errandonea, D., Meng, Y., Somayazulu, M., & Häusermann, D. (2005). Pressure-induced transition in titanium metal: a systematic study of the effects of uniaxial stress. Physica B: Condensed Matter, 355(1-4), 116-125. doi:10.1016/j.physb.2004.10.030Klotz, S., Paumier, L., Le March, G., & Munsch, P. (2009). The effect of temperature on the hydrostatic limit of 4:1 methanol–ethanol under pressure. High Pressure Research, 29(4), 649-652. doi:10.1080/08957950903418194Errandonea, D., & Manjón, F. J. (2008). Pressure effects on the structural and electronic properties of ABX4 scintillating crystals. Progress in Materials Science, 53(4), 711-773. doi:10.1016/j.pmatsci.2008.02.001Lacomba-Perales, R., Errandonea, D., Meng, Y., & Bettinelli, M. (2010). High-pressure stability and compressibility ofAPO4(A=La, Nd, Eu, Gd, Er, and Y) orthophosphates: An x-ray diffraction study using synchrotron radiation. Physical Review B, 81(6). doi:10.1103/physrevb.81.064113Crichton, W. A., Parise, J. B., Antao, S. M., & Grzechnik, A. (2005). Evidence for monazite-, barite-, and AgMnO4(distorted barite)-type structures of CaSO4at high pressure and temperature. American Mineralogist, 90(1), 22-27. doi:10.2138/am.2005.1654Huang, T., Shieh, S. R., Akhmetov, A., Liu, X., Lin, C.-M., & Lee, J.-S. (2010). Pressure-induced phase transition inBaCrO4. Physical Review B, 81(21). doi:10.1103/physrevb.81.214117Zhang, F. X., Wang, J. W., Lang, M., Zhang, J. M., Ewing, R. C., & Boatner, L. A. (2009). High-pressure phase transitions ofScPO4andYPO4. Physical Review B, 80(18). doi:10.1103/physrevb.80.184114Panchal, V., Garg, N., & Sharma, S. M. (2006). Raman and x-ray diffraction investigations on BaMoO4under high pressures. Journal of Physics: Condensed Matter, 18(16), 3917-3929. doi:10.1088/0953-8984/18/16/00

High-pressure structural study of the scheelite tungstates CaWO4 and SrWO4

Angle-dispersive x-ray diffraction (ADXRD) and x-ray absorption near edge structure (XANES) measurements have been performed in the AWO4 tungstates CaWO4 and SrWO4 under high pressure up to approximately 20 GPa. Similar phase transitions and phase transition pressures have been observed for both tungstates using the two techniques in the studied pressure range. Both materials are found to undergo a pressure-induced scheelite-to-fergusonite phase transition under sufficiently hydrostatic conditions. Our results are compared to those found previously in the literature and supported by ab initio total energy calculations. From the total energy calculations we have also predicted a second phase transition from the fergusonite structure to a new structure identified as Cmca. Finally, a linear relationship between the charge density in the AO8 polyhedra of ABO4 scheelite-related structures and the bulk modulus is discussed and used to predict the bulk modulus of other materials, like zircon.Comment: 52 pages, 9 figure, 4 table

High-pressure phase diagram of ZnSexTe1–x alloys.

We have performed high-pressure energy dispersive x-ray diffraction experiments in ZnSexTe1–x alloys (x = 0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) in order to establish their pressure-composition phase diagram, and characterize the equation of state of all the involved phases. We conclude that the electronic energy-volume dependence is similar in all compounds. The differences observed in the stability range of the cinnabar and Cmcm phases should then be discussed in terms of other factors, as the presence of energy barriers (cinnabar) or dynamical instabilities (Cmcm). We also argue that the cinnabar phase found is similar for all compositions. Finally we discuss the different compressibility observed in the Cmcm and rocksalt phases

Experimental and theoretical study on the optical properties of LaVO4 crystals under pressure

We report optical absorption and luminescence measurements in pure and trivalent neodymium (Nd3+) doped LaVO4 crystals up to 25 GPa. Nd3+ luminescence has been employed as a tool to follow the structural changes in the crystal. We also present band-structure and crystal-field calculations that provide the theoretical framework to accurately explain the observed experimental results. In particular, both optical absorption and luminescence measurements evidence that a phase transition takes place close to 12 GPa. They also provide information on the pressure dependence of the band-gap as well as the emission lines under compression. We found drastic changes in the optical properties of LaVO4 when the phase transition to a BaWO4-II structure occurs, which can be related to changes in the coordination number of vanadium ions and in the local sites of Nd3+. Reported results are analyzed in comparison with those of previous X-ray diffraction and Raman experiments, as well as with the features of related compounds. For the first time, a consistent picture is reported explaining the behavior of the optical and electronic properties of LaVO4 at high-pressures