Observation of a sample-dependent 37 K anomaly on the lattice parameters of strontium titanate (original) (raw)
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The SrTiO $ _3 $ displacive transition revisited by Coherent X-ray Diffraction
We present a Coherent X-ray Diffraction study of the antiferrodistortive displacive transition of SrTiO3, a prototypical example of a phase transition for which the critical fluctuations exhibit two length scales and two time scales. From the microbeam x-ray coherent diffraction patterns, we show that the broad (short-length scale) and the narrow (long-length scale) components can be spatially disentangled, due to 100 µm-scale spatial variations of the latter. Moreover, both components exhibit a speckle pattern, which is static on a ∼10 mn time-scale. This gives evidence that the narrow component corresponds to static ordered domains. We interpret the speckles in the broad component as due to a very slow dynamical process, corresponding to the well-known central peak seen in inelastic neutron scattering. PACS numbers: 61.10.-i,68.35.Rh;77.84.Dy
Lowering of ground state induced by core-shell structure in strontium titanate
Physical Review B, 2016
A new ground state of textbook compound strontium titanate (SrTiO 3) is obtained by inducing a specific core-shell structure of the particles. Using a combination of high energy synchrotron and neutron diffraction, we demonstrate a lowering of the ferroelastic ground state towards a new antiferrodistortive phase, accompanied with strong shifts of the critical temperature. This new phase is discussed within the Landau theory and compared with the situation in thin films and during pressure experiments. The crucial competition between particle shape anisotropy, surface tension, and shear strain is analyzed. Inducing a specific core-shell structure is therefore an easy way to tailor structural properties and to stabilize new phases that cannot exist in bulk material, just like film deposition on a substrate.
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An electric field-induced reversible structural distortion at room temperature is observed at an as-cut singlecrystalline SrTiO 3 [001] wafer. The structural changes have been characterised in situ by means of X-ray diffraction. It is concluded that the effect requires a distortion of the cubic crystal structure, as it was present only at the rough unpolished side of the wafer. The appearance of the phenomenon was found to depend on the direction of the electric field. Structural changes, depending on the electric field strength, were completely reversible. Regarding the possible electromechanical coupling phenomena, the piezoelectric and electrostrictive effects have to be considered. Cubic SrTiO 3 belongs to the centrosymmetric point group m3m; hence, no piezoelectric effect is present, whereas second-order effects like electrostriction may occur. Peculiarities arising as a result of the special constraints are discussed.
2020
The properties of quantum materials are commonly tuned using experimental variables such as pressure, magnetic field and doping. Here we explore a different approach: irreversible, plastic deformation of single crystals. We show for the superconductor SrTiO$_3$ that compressive plastic deformation induces low-dimensional superconductivity significantly above the superconducting transition temperature ($T_c$) of undeformed samples, with evidence of superconducting correlations at temperatures two orders of magnitude above the bulk TcT_cTc. The superconductivity enhancement is correlated with the appearance of self-organized dislocation structures, as revealed by diffuse neutron and X-ray scattering. We also observe signatures of deformation-induced quantum-critical ferroelectric fluctuations and inhomogeneous ferroelectric order via Raman scattering. These results suggest that the strain surrounding the self-organized dislocation structures induces local ferroelectricity and quantum-cr...
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A full-potential linearized-augmented plane-wave calculation was used to study structural and electronic properties of defected SrTiO 3 with two concentrations of oxygen vacancies. These properties were found to remarkably depend on the oxygen vacancy concentration. The defect states associated with oxygen vacancies are identified within the energy gap. The ground state properties, equilibrium lattice constants, bulk moduli, the formation energy, densities of electron states, band structures and charge density are determined and discussed for this compound. It is found that an oxygen vacancy creates more localized in-gap states. With increasing oxygen deficiency, the electrons left behind by oxygen removal not only localize on Sr (Ti) 3d orbitals but also on the vacancy sites. Model structures of 2 Â 2 Â n (n = 1, 2, 3 and 4) supercells are used.
Core-Shell structure induces new ground states in strontium titanate
HAL (Le Centre pour la Communication Scientifique Directe), 2017
Hyper-Raman scattering (HRS) is a non-linear spectroscopy sensitive to all polar excitations, in particular the soft modes inactive in Raman. HRS has been applied to nano-ceramics of strontium titanate (SrTiO 3) of controlled grain size. Contrary to infrared absorption which sees an average medium, the vibrational responses of the core and the shell(s) are split in HRS, allowing thereby probing the structural and dielectric properties of the two subsystems. The resulting structural model successfully reproduces the effective dielectric permittivity measured by dielectric experiments [1]. These results confirm the strong, but still under-exploited, potentialities of HRS for the investigation of polar materials [2]. We also demonstrate that a new ground state can be obtained by tailoring the core-shell structure of the particles. High energy X-rays at synchrotron combined to neutron diffraction and HRS revealed a lowering of the ferroelastic ground state towards a new antiferrodistortive phase, accompanied with strong shift of the critical temperature [3,4]. This new phase is discussed within the Landau theory, and the crucial competition between particle shape anisotropy, surface tension, and shear strain is analyzed as well. This shows that controlling the core-shell structure provides an easy way to stabilize new phases that cannot exist in bulk material, just like film deposition on a substrate.
Crystal Dislocations: Their Impact on Physical Properties of Crystals
Crystals
It is rare to find technical applications involving a material of any crystal structure that is not impacted by dislocations—which affect the material’s mechanical properties, interfaces, martensitic phase transformations, crystal growth, and electronic properties, to name a few. [...]
Crystals
Oxide materials have the potential to exhibit superior mechanical properties in terms of high yield point, high melting point, and high chemical stability. Despite this, they are not widely used as a structural material due to their brittle nature. However, this study shows enhanced room-temperature plasticity of strontium titanate (SrTiO 3) crystals through the control of the chemical composition. It is shown that the deformation behavior of SrTiO 3 crystals at room temperature depends on the Sr/Ti ratio. It was found that flow stresses in deforming SrTiO 3 crystals grown from a powder with the particular ratio of Sr/Ti = 1.04 are almost independent of the strain rate because of the high mobility of dislocations in such crystals. As a result, the SrTiO 3 crystals can deform by dislocation slip up to a strain of more than 10%, even at a very high strain rate of 10% per second. It is thus demonstrated that SrTiO 3 crystals can exhibit excellent plasticity when chemical composition in the crystal is properly controlled.
Journal of Physics: Condensed Matter, 1998
The transition between the cubic and tetragonal phase in SrTiO 3 shows an excess specific heat of 0.0035 J g −1 K −1 . Comparison between the temperature evolution of the excess entropy S = (C/T ) dT and the structural order parameter Q shows S ∝ Q 2 within experimental errors (γ = 1.004±0.006). The apparent order parameter exponentβ = 0.35±0.02 was confirmed and analysed using a Landau-type expression for the excess Gibbs free energy G = Aθ s (coth(θ s /T ) − coth(θ s /T c ))Q 2 + 1 4 BQ 4 + 1 6 CQ 6 with A = 0.70 J K −1 mol −1 , B = 31.22 J mol −1 , C = 42.17 J mol −1 , T c = 105.65 K and θ s = 60.75 K. The closeness to the tricritical point is seen by B < C; all thermodynamic data between 85 K and T c could be described selfconsistently using this approach although small deviations cannot be excluded in a temperature interval of less than 1 K around T c and a small tail of excess entropy at T > T c .