Phase Transformations

[Summary by Dr. Manish Kumar]

 

When a high energy ion (>10 keV/amu) slows down in matter, strong ionization of the target atoms located along the ion trajectory occurs and highly excited electrons are ejected. The effect of such high electronic energy deposition on transition metal oxides, semiconductors and metals induces the phase transformations of various kinds which have been extensively studied at the Pelletron accelerator of IUAC Delhi.   

The phase transformation of orthogonal Ag2O3 into cubic Ag phase has been reported when sol-gel derived Ag2O3:ZrO2 films were irradiated with 100 MeV Ag ions at a fluence of ≥3×1012 ions/cm2 [1]. Such phase transformation was particularly interesting for the evolution and tailoring of plasmonic properties in nanocomposites via swift heavy ion irradiation.  

In TiO2, though the thermal annealing is known to cause transformation from anatase to rutile phase in a temperature interval of 700–900 °C, a sizable volume fraction of anatase still remains even after annealing at 1000 °C. Irradiations by 200 MeV Ag ions on the other hand suppressed the anatase phase and almost phase pure rutile TiO2 could be obtained at a fluence of 3x1012 ions cm−2 [2] .  

In spray pyrolysis derived thin films, transformation from metastable state to a different stable phase has been observed [3, 4]. When irradiated with 100 MeV Ag ions, CdS thin films show a phase transformation from the metastable cubic to hexagonal phase. At the highest irradiation fluence, a significant amount of compressive strain is created in these films [3]. In polycrystalline CdTe films, transformation of the metastable hexagonal regions into stable cubic phase was found [4].  

In calcite single crystals, 120 MeV Au9+  ions irradiation induces the phase transformation from calcite to vaterite phases at fluences ≥5×1012  ion/cm2 [5] .  

Phase transformation of semiconductor sub-oxides in to semiconductor nanocrystallites can be obtained with the help of swift heavy ions [6, 7] . When silicon oxide (SiOx) are irradiated with 100 MeV Ni ions at fluences varying from 1×1012 to 5×1013 ions/cm2, It induces the crystallization of nanocrystalline silicon embedded in SiO2[6] . Similar kind of phase transformation from SiO2 to Si-nanoprecipitates is reported when irradiated with 70 MeV Si-beam [7] .  

It was found that irradiation by 190 MeV Ag ions on Fe3O4 thin films grown on MgO <100> substrate loose the epitaxial relationship of the films with the substrate along with a phase transformation from magnetite to more oxidized magnetite phase (i.e. maghemite) [8] .  

Apart from these reports, swift heavy ion irradiation induced phase transformations in ThGeO4 [9], YBa2Cu3O7−y thin films [10], ZnS nanocrystalline thin films [11] and Perovskite Superconductor materials [12] are also reported.

 

 

References  

  1. Manish Kumar, P.K. Kulriya, J.C. Pivin, and D.K. Avasthi, "Evolution and tailoring of plasmonic properties in Ag:ZrO2 nanocomposite films by swift heavy ion irradiation", J. Appl. Phys. 109 (2011) 044311. 
  2. H. Rath, P. Dash, T. Som, P.V. Satyam, U.P. Singh, P.K. Kulriya, D. Kanjilal, D.K. Avasthi, and N.C. Mishra, "Structural evolution of TiO2 nanocrystalline thin films by thermal annealing and swift heavy ion irradiation", J. Appl. Phys. 105 (2009) 074311. 
  3. V.V. Ison, A. Ranga Rao, V. Dutta, P.K. Kulriya, D.K. Avasthi, and S.K. Tripathi, "Swift heavy ion induced structural changes in CdS thin films possessing different microstructures: A comparative study", J. Appl. Phys. 106 (2009) 023508. 
  4. V.V. Ison, A. Ranga Rao, V. Dutta, P.K. Kulriya, D.K. Avasthi, "Swift heavy ion induced phase transition in CdTe films deposited by spray pyrolysis in presence of electric field", NIMB 267 (2009) 2480. 
  5. H. Nagabhushana, B.M. Nagabhushana, B.N. Lakshminarasappa, Fouran Singh, R.P.S. Chakradhar, "Swift heavy ion irradiation induced phase transformation in calcite single crystals" Solid State Communications, 149 (2009) 1905. 
  6. Prajakta S. Chaudhari, Tejashree M. Bhave, D. Kanjilal, and S. V. Bhoraskar, "Swift heavy ion induced growth of nanocrystalline silicon in silicon oxide", J. Appl. Phys. 93 (2003) 3486. 
  7. T. Mohanty, A Pradhan, S. Gupta, D Kanjilal, "Nanoprecipitation in transparent matrices using an energetic ion beam", Nanotechnology 15 (2004) 1620–1624. 
  8. Ravi Kumar, R. J. Choudhary, S. I. Patil, Shahid Husain, J. P. Srivastava et al., " Structural, electrical transport, magnetization, and 1f noise studies in 200 MeV Ag ion irradiated La0.7Ce0.3MnO3 thin films", J. Appl. Phys. 96 (2004) 7383. 
  9. M.K. Patel, D.K. Avasthi, P.K. Kulriya, S. Kailas, J.C. Pivin, A.K. Tyagi, and V. Vijayakumar, "Swift heavy ion induced structural modifications in zircon and scheelite phases of ThGeO4", NIMB 268 (2010) 42. 
  10. R. Biswal, J. John, P. Mallick, B.N. Dash, P.K. Kulriya, D.K. Avasthi, D. Kanjilal, D. Behera, T. Mohanty, P. Raychaudhuri, and N.C. Mishra, "200 MeV silver ion irradiation induced structural modification in YBa2Cu3O7−y thin films at 89 K: An in situ x-ray diffraction study", J. Appl. Phys. 106 (2009) 053912.
  11. S.P. Patel, S.A. Khan, A.K. Chawla, R. Chandra, J.C. Pivin, D. Kanjilal, L. Kumar, "Structural phase diagram for ZnS nanocrystalline thin films under swift heavy ion irradiation", Physica B 406 (2011) 4150. 
  12. U. Tiwari, N. Sen, A. K. Bandyopadhyay, D. Kanjilal and P. Sen, "Phase Transition in a Perovskite Superconductor by Radiation-Induced Lattice Excitations", Europhys. Lett. 25 (1994) 705.
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