Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMonte Carlo Study of Relaxor Systems: A Minimum Model for Pb(In$_{1/2}$Nb$_{1/2}$)O$_3$}
87
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We examine a simple model for Pb(In$_{1/2}$Nb$_{1/2}$)O$_3$ (PIN), which includes both long-range dipole-dipole interaction and random local anisotropy. A improved algorithm optimized for long-range interaction has been applied for efficient large-scale Monte Carlo simulation. We demonstrate that the phase diagram of PIN is qualitatively reproduced by this minimum model. Some properties characteristic of relaxors such as nano-scale domain formation, slow dynamics and dispersive dielectric responses are also examined.
rate research
Read More
We investigate the low temperature behaviour of Pb(In$_{1/2}$Nb$_{1/2}$)O$_{3}$-Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$ using dielectric permittivity measurements. We compare single crystal plates measured in the [001] and [111] directions with a polycrystalline ceramic of the same composition. Poled crystals behave very differently to unpoled crystals, whereas the dielectric spectrum of the ceramic changes very little on poling. A large, frequency dependent dielectric relaxation seen in the poled [001] crystal around 100 K is much less prominent in the [111] crystal, and doesnt occur in the ceramic. Preparation conditions and the microstructure of the material play a role in the low temperature dynamics of relaxor-ferroelectric crystals.
We report the spontaneous decay of a soft, optical phonon in a solid. Using neutron spectroscopy, we find that specific phonon lifetimes in the relaxor PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$ are anomalously short within well-defined ranges of energy and momentum. This behavior is independent of ferroelectric order and occurs when the optical phonon with a specific energy and momentum can kinematically decay into two acoustic phonons with lower phase velocity. We interpret the well-known relaxor waterfall effect as a form of quasiparticle decay analogous to that previously reported in quantum spin liquids and quantum fluids.
Ba(Fe$_{1/2}$Nb$_{1/2}$)O$_{3}$ (BFN) ceramics are considered to be a potential candidate for technological applications owing to their high dielectric constant over a wide range of temperature values. However, there exists considerable discrepancy over the structural details. We address this discrepancy through a comparative analysis of the earlier reported structures and combined X-Ray Diffraction (XRD) at room temperature and Neutron Powder Diffraction (NPD) measurements in the range of 5K up to room temperature. Our study reveals a cubic structure with space group $Pmbar{3}m$ at all measured temperatures. The local environment of the Fe ions is investigated using X-ray Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) technique. A detailed investigation of the electronic properties of the synthesized BFN ceramics is carried out by combination of theoretical and experimental tools: X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and density functional theory (DFT) within GGA$+U$. The bandgap is estimated using the diffuse reflectance measurements in the UV-Vis-NIR range and an appropriate value of the electron-electron correlation strength $U$ is estimated based on the UV-Vis-NIR and the XAS spectra.
We investigate the critical relaxational dynamics of the S=1/2 Heisenberg ferromagnet on a simple cubic lattice within the Handscomb prescription on which it is a diagrammatic series expansion of the partition function that is computed by means of a Monte Carlo procedure. Using a phenomenological renormalization group analysis of graph quantities related to the spin susceptibility and order parameter, we obtain precise estimates for the critical exponents relations $gamma / u = 1.98pm 0.01 $ and $beta / u = 0.512 pm 0.002$ and for the Curie temperature $k_BT_c/J = 1.6778 pm 0.0002$. The critical correlation time of both energy and susceptibility is also computed. We found that the number of Monte Carlo steps needed to generate uncorrelated diagram configurations scales with the systems volume. We estimate the efficiency of the Handscomb method comparing its ability in dealing with the critical slowing down with that of other quantum and classical Monte Carlo prescriptions.
The crystal structure of the PbMg$_{1/3}$Ta$_{2/3}$O$_3$ (PMT) relaxor ferroelectric was studied under hydrostatic pressure up to $sim 7$ GPa by means of powder neutron diffraction. We find a drastic pressure-induced decrease of the lead displacement from the inversion centre which correlates with an increase by $sim$ 50 % of the anisotropy of the oxygen temperature factor. The vibrations of the Mg/Ta are, in contrast, rather pressure insensitive. We attribute these changes being responsible for the previously reported pressure-induced suppression of the anomalous dielectric permittivity and diffuse scattering in relaxor ferroelectrics.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
