Ion Irradiation Induced Phase Transformation Research Articles

Investigations on ion irradiation induced microstructural changes in Gd2O3 nanorods

Ion irradiation induced phase transformations in Gd2O3 nanorods dispersed on TEM grids, are investigated using synchrotron X-ray diffraction and transmission electron microscopy. Ion irradiation induced cubic (C) to monoclinic (B) phase transformation is observed in Gd2O3 nanorods. Gd2O3 nanorods are partially transformed to monoclinic phase at 0.63 dpa (5 × 1016 ions/cm2) itself. The C→B phase transformation is reconstructive type transformation where the role of O-vacancies and diffusion are very important. During He+ ion irradiation, the displacement cascades produced O-vacancies and during the non-melting thermal spike regime, diffusion was assisted and it resulted in the phase transformation. In addition to phase transformation, TEM investigations shows formation of amorphous carbon layer around the nanorods and welding of the nanorods, upon ion irradiation. These observations are explained based on the mechanisms of GOLF (giant onion like fullerene) formation and the localized surface melting during thermal spike.

Combined experimental and first-principles studies of structural and physical properties of β-Ti3SiC2

MAX phase materials have shown a series of interesting, even sometimes unusual, properties and exhibited combined attributes of both metals and ceramics, which are due to their “layered ternary transition metal carbides” structures. In the process of studying the multistage phase transformation of 312-MAX phase materials, we found that there were some confusions and mistakes when describing the crystal structures of the β-phase in the existing literature. In order to clarify their structural and physical properties, the β-phase Ti3SiC2 materials have been prepared by using 500 keV He2+-ion irradiation-induced phase transformation and examined by first-principles calculations and Rietveld analysis of grazing incidence x-ray diffraction patterns. Two accurate descriptions of the β-Ti3SiC2 structure are given here. In order to avoid confusion again, it is recommended to use one of the two descriptions uniformly. In addition, some physical properties parameters of β-Ti3SiC2 have been calculated and compared, which also confirmed the correctness of the structure description. Finally, the vacancy formation energies of β-Ti3SiC2 have been predicted and discussed in detail from the points of phase stability and transformation for the first time.

Ion irradiation induced phase transformation in gold nanocrystalline films

Gold is a noble metal typically stable as a solid in a face-centered cubic (FCC) structure under ambient conditions; however, under particular circumstances aberrant allotropes have been synthesized. In this work, we document the phase transformation of 25 nm thick nanocrystalline (NC) free-standing gold thin-film via in situ ion irradiation studied using atomic-resolution transmission electron microscopy (TEM). Utilizing precession electron diffraction (PED) techniques, crystallographic orientation and the radiation-induced relative strains were measured and furthermore used to determine that a combination of surface and radiation-induced strains lead to an FCC to hexagonal close packed (HCP) crystallographic phase transformation upon a 10 dpa radiation dose of Au4+ ions. Contrary to previous studies, HCP phase in nanostructures of gold was stabilized and did not transform back to FCC due to a combination of size effects and defects imparted by damage cascades.

Role of the X and n factors in ion-irradiation induced phase transformations of Mn+1AXn phases

Phase transitions induced in hcp Mn+1AXn phases (Ti2AlN, Ti2AlC, and Ti4AlN3) by 1 MeV Au+ ion irradiation were investigated, over a series of ion fluences ranging from 1 × 1014 to 2 × 1016 ions cm−2, by transmission electron microscopy (TEM) and synchrotron grazing incidence X-ray diffraction (GIXRD). Irradiation-induced structural evolutions were observed using high-resolution TEM (HRTEM) imaging and selected area electron diffraction (SAED). Based on phase contrast imaging and electron diffraction pattern (EDP) simulations, the atomic-scale mechanisms for the phase transitions were determined. Transformations of the initial hcp phases to the intermediate γ-phases and fcc phases were driven by the formation of Ti/Al antisite defects and extended stacking faults induced by ion irradiation. By comparing the transformation behavior of Ti2AlN with that of Ti2AlC and Ti4AlN3 under the same irradiation conditions, using both the experimental data and first-principles calculations, the role of the X and n parameters in the radiation responses of Mn+1AXn phases were elucidated. The susceptibilities of materials in this Ti-Al-X (X = C, N) system to irradiation-induced phase transitions were determined with respect to the bonding characteristics and compositions of these MAX phases. Ti2AlC is slightly less susceptible to the radiation-induced phase transformation than Ti2AlN, which is attributed to the stronger Ti-Al bond covalency in Ti2AlN. Ti4AlN3 is more resistant to radiation-induced phase transformations than is Ti2AlN, due to the lower Al content and lower anion vacancy ratio in the irradiation-induced solid solution phases.

Swift heavy ion irradiation induced phase transformation in undoped and niobium doped titanium dioxide composite thin films

Study reports the effect of swift heavy ion (SHI) irradiation induced phase transformation in undoped and Niobium doped anatase TiO2 composite thin films. Investigations were carried out at different densities of electronic excitations (EEs) using 120MeV Ag and 130MeV Ni ions irradiations. Films were initially annealed at 900°C and results revealed that undoped films were highly stable in anatase phase, while the Nb doped films showed the composite nature with the weak presence of Niobium penta-oxide (Nb2O5) phase. The effect at low density of EEs in undoped film show partial anatase to rutile phase transformation; however doped film shows only further growth of Nb2O5 phase beside the anatase to rutile phase transformation. At higher density of EEs induced by Ag ions, registered continuous ion track of ∼3nm in lattice which leads to nano-crystallization followed by decomposition/amorphization of rutile TiO2 and Nb2O5 phases in undoped and doped films, respectively. However, Ni ions are only induced discontinuous sequence of ion tracks with creation of damage and disorder and do not show amorphization in the lattice. The in-elastic thermal spike calculations were carried out for anatase TiO2 phase to understand the effect of EEs on anatase to rutile phase transformation followed by amorphization in NTO films in terms of continuous and discontinuous track formation by SHI irradiation.

Ion irradiation-induced phase transformation mechanisms in Y2O3 thin films

This work studies the ion irradiation-induced phase transformations in thin films of yttrium oxide. The films were deposited using an ion beam sputtering technique that allows the control of the order/disorder of the microstructure. As-deposited (disordered) and annealed (ordered) samples were irradiated by xenon ions at different energies and doses. Two different structural phase transformations were observed: cubic/amorphous-like and cubic/monoclinic. In both cases, it is shown that the pristine structure is of prime importance in the transformation process. The phase transformations are analysed in terms of structural extended defect nucleation originating from the oxygen network behaviour, which leads to polygonisation up to a nanocrystallite-like structure, followed by a phase transformation into a monoclinic structure.

Ion irradiation-induced phase transformations in bixbyite-fluorite related oxides: The role of dislocation loop nucleation

The ion irradiation induced phase transformations of bixbyite-fluorite related oxides have been studied with thin films of Y2O3 grown on Si and SrTiO3 by an ion beam sputtering technique which allows to control the microstructure and stresses within the film. Y2O3 thin films are ion-irradiated with an xenon beam in an energy range 60–380keV at a fluence of 4.4×1015 Xe/cm2 at 80K. Depending on the energy of the xenon beam two different structural phase transformations are observed: cubic to nanocrystalline/amorphous and cubic to monoclinic phase transformations. The phase transformation are analysed in terms of structural extended defect nucleation like prismatic dislocation loops due to the oxygen network behaviour under ion irradiation.

Swift heavy ion irradiation-induced phase transformation in oxide materials

The present study briefly reviews the effect of ion irradiation in inducing structural transformation in oxide materials. The effect of ion irradiation on simple systems such as Y2O3, CuO, ZrO2, HfO2 and TiO2 and a few members of the high T c cuprate superconductor family are examined. Some of the phase transformations induced are shown to be uniquely possible by swift heavy ion (SHI) irradiation and cannot be achieved by thermal annealing. In nanoparticle thin films of TiO2, irradiation is shown to completely transform the anatase phase to a rutile phase, whereas thermal annealing even at 1273 K could not lead to complete conversion. The thermal spike model of ion–matter interaction is shown to explain ion irradiation-induced phase transformation in most of the oxide materials. In a more complex system like the high T c superconductor YBa2Cu3O7, secondary electrons radially emerging from the path of SHI are shown to induce selective disorder in the CuO basal planes without affecting the net oxygen content. This unique feature of SHI is not achievable by any other techniques.

Ion irradiation-induced phase transformations in δ–γ–β phases of Sc 2O 3–ZrO 2 mixtures

The purpose of this study is to investigate the role of stoichiometry in crystalline structure transformations in derivative fluorite compounds known as δ–γ–β phases in Sc 2O 3–ZrO 2 phase diagram. Different composition polycrystalline δ-Sc 4Zr 3O 12, γ-Sc 2Zr 5O 13 and β-Sc 2Zr 7O 17 samples were synthesized by mixing 40% Sc 2O 3 + 60% ZrO 2, 16.67% Sc 2O 3 + 83.33% ZrO 2, or 12.5% Sc 2O 3 + 87.5% ZrO 2, respectively. The pressed and polished pellets of these compounds were then irradiated under liquid nitrogen temperature with 200 keV Ne + ions at a dose rate of ∼1 × 10 12 ions/cm 2/s. An order-to-disorder (O–D) transformation was observed for all compositions, as determined using grazing incidence X-ray diffraction (GIXRD) at an incident angle of 0.25°. The O–D transformation threshold dose for δ-Sc 4Zr 3O 12 (∼0.2 dpa) was found to be noticeably higher than that for γ-Sc 2Zr 5O 13 and β-Sc 2Zr 7O 17 (∼0.04 dpa) based on both GIXRD and cross-sectional transmission electron microscopy (TEM) measurements. However, due to experimental difficulty and uncertainty, our GIXRD and TEM data were unable to conclusively confirm that the O–D transformation threshold dose for γ-Sc 2Zr 5O 13 is in fact slightly higher than that for β-Sc 2Zr 7O 17 as expected from the phase diagram of Sc 2O 3–ZrO 2 system.

Swift heavy ion irradiation induced phase transformation in calcite single crystals

Ion irradiation induced phase transformation in calcite single crystals have been studied by means of Raman and infrared spectroscopy using 120 MeV Au 9+ ions. The observed bands have been assigned according to group theory analysis. For higher fluence of 5×10 12 ion/cm 2, an extra peak on either side of the 713 cm −1 peak and an increase in the intensity of 1085 cm −1 peak were observed in Raman studies. FTIR spectra exhibit extra absorption bands at 674, 1589 cm −1 and enhancement in bands at 2340 and 2374 cm −1 was observed. This might be due to the phase transformation from calcite to vaterite. The damage cross section ( σ ) for all the Raman and FTIR active modes was determined. The increase of FWHM, shift in peak positions and appearance of new peaks indicated that calcite phase is converted into vaterite.

Swift heavy ion induced phase transition in CdTe films deposited by spray pyrolysis in presence of electric field

CdTe polycrystalline thin films possessing hexagonal phase regions are obtained by spray deposition in presence of a high electric field. Thin film samples are irradiated with 100 MeV Ag ions using Pelletron accelerator to study the swift heavy ion induced effects. The ion irradiation results in the transformation of the metastable hexagonal regions in the films to stable cubic phase due to the dense electronic excitations induced by beam irradiation. The phase transformation is seen from the X-ray diffraction patterns. The band gap of the CdTe film changes marginally due to ion irradiation induced phase transformation. The value changes from 1.47 eV for the as deposited sample to 1.44 eV for the sample irradiated at the fluence 1 × 10 13 ions/cm 2. The AFM images show a gradual change in the shape of the particles from rod shape to nearly spherical ones after irradiation.

Why ion irradiation does not lead to the same structural changes in normal spinels ZnAl2O4, MgAl2O4 and MgCr2O4?

Ion irradiation induced phase transformations in three normal spinel compounds MgAl2O4, MgCr2O4 and ZnAl2O4 were investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The structural and microstructural changes occurring in these three systems are described. Irradiation acts at the atomic and mesoscopic scales in different ways. At the atomic scale it produces the inversion of the cations in the structure. At the mesoscopic scale it produces a change of the size of the diffracting domains, responsible for the colossal changes in the observed X-ray diffraction patterns.

Characterization of an ion irradiation induced phase transformation in monoclinic zirconia

Ion irradiation damage experiments were performed on polycrystalline samples of monoclinic, sub-stoichiometric zirconia (ZrO 1.98). Following irradiation with 300 keV Kr 2+ ions, the monoclinic phase was gradually replaced by a new phase. Grazing incidence X-ray diffraction (GIXRD) measurements revealed that the radiation-induced phase is either a tetragonal or cubic polymorph of zirconia. This phase appeared at peak displacement damage doses as low as 1.8 displacements per atom (dpa). Raman spectroscopy (RS) measurements were performed in an attempt to discern the nature of the transformed irradiated material, but these measurements in the confocal geometry failed to unambiguously establish the nature of the phase transformation. Transmission electron microscopy (TEM) experiments and particularly microdiffraction (μD) measurements revealed that in a sample irradiated to a fluence of 1 × 10 20 Kr/m 2, the transformed zirconia possesses a tetragonal structure. This was evidenced by the appearance of (1 1 2)-type Bragg reflections (indexed according to a “face-centered” unit cell) in the irradiated sample material. These (1 1 2) reflections are allowed in a tetragonal structure, while they are forbidden in cubic zirconia. Finally, additional GIXRD measurements on Kr 2+ ion irradiated zirconia samples revealed very weak intensities at the diffraction position corresponding to a (1 1 2) tetragonal zirconia reflection.

Correlation of Formation Enthalpies with Critical Amorphization Temperature for Pyrochlore and Monazite

AbstractSystematic studies of a series of RE-titanate pyrochlore single crystals determined the formation enthalpies, ΔH0f-ox, and the critical amorphization temperature, Tc, the temperature above which the crystal can no longer be amorphized. A negative linear correlation was observed between ΔH0f-ox and Tc. In general as the cation radius ratio, RA/RB, decreases the formation enthalpy becomes less exothermic, i.e. the pyrochlore structure becomes less thermodynamically stable while the susceptibilty to ion beam-induced amorphization decreases. The opposite relation, i.e. a positive linear correlation between ΔH0f-ox and Tc was observed for a series of REPO4 single crystals with both the monazite and xenotime structures. Both relations can be understood in terms of pyrochlore and orthophosphate crystal chemistry, their formation of point defects, and the role of ion-irradiation induced phase transformations.

Ion irradiation-induced phase transformation of pyrochlore and zirconolite

Pyrochlore (Gd 2Ti 2O 7) and zirconolite (CaZrTi 2O 7) were irradiated with 1.5 MeV Xe +, 1.0 MeV Kr +, and 0.6 MeV Ar + at temperatures from 20 to 1073 K. Critical amorphization dose increased with increasing temperature. Heavier ion irradiation increased the critical temperature. The extrapolated critical temperatures for amorphization were calculated as: 1300, 1100 and 950 K for pyrochlore irradiated with 1.5 MeV Xe +, 1.0 MeV Kr + and 0.6 MeV Ar +, respectively; 710 and 654 K for zirconolite irradiated with 1.5 MeV Xe + and 1.0 MeV Kr +, respectively. At the early stage of irradiation, pyrochlore transformed to a disordered fluorite structure; monoclinic zirconolite first transformed to partially disordered cubic pyrochlore structure followed by a disordered fluorite structure.

Ion irradiation-induced phase transformation in AlCuCoGe decagonal quasicrystal

The ion irradiation-induced phase transformation in a AlCuCoGe decagonal quasicrystal has been studied by means of in situ transmission electron microscopy. Prior to ion irradiation, typical single decagonal quasicrystalline HRTEM images and electron diffraction patterns along the tenfold axis were observed. The HRTEM image clearly showed the decagonal quasicrystal structure and revealed no apparent defects in the unirradiated material. After a 1.5 MeV Xe + ion irradiation to a dose of 4.3 × 10 14 ions/cm 2, electron diffraction and HRTEM images indicated that the original, single quasicrystal had transformed into amorphous and bcc crystalline components. Moreover, the amorphous component had the same composition as the original quasicrystal, and the bcc crystalline component lacked aluminum as compared with the quasicrystal. The crystalline component was much more resistant to amorphization than the quasicrystalline structure. The phase transformation and separation observed in the Xe + ion irradiated AlCuCoGe quasicrystal were due to irradiation-induced defect accumulation and compositional segregation. During the annealing of the Xe + ion-irradiated specimen, the electron diffraction pattern of the crystalline phase component did not change with the increasing temperature. However, a transition from amorphous-to-quasicrystal was observed during annealing at different temperatures.