Studies at high pressures and temperatures are helpful for understanding the physical properties of the solid state, including such classes of materials as, metals, semiconductors, superconductors, or minerals. In particular, the phase behaviour of ABX4 scintillating materials is a challenging problem with many implications for other fields including technological applications and Earth and planetary sciences. A great progress has been done in the last years in the study of the pressure-effects on the structural and electronic properties of these compounds. In particular, the high-pressure structural sequence followed by these compounds seems now to be better understood thanks to recent experimental and theoretical studies. Here, we will review studies on the phase behaviour of different ABX4 scintillating materials. In particular, we will focus on discussing the results obtained by different groups for the scheelite-structured orthotungstates, which have been extensively studied up to 50 GPa. We will also describe different experimental techniques for obtaining reliable data at simultaneously high pressure and high temperature. Drawbacks and advantages of the different techniques are discussed along with recent developments involving synchrotron X-ray diffraction, Raman scattering, and ab initio calculations. Differences and similarities of the phase behaviour of these materials will be discussed, on the light of Fukunaga and Yamaoka’s and Bastide’s diagrams, aiming to improve the actual understanding of their high-pressure behaviour. Possible technological and geophysical implications of the reviewed results will be also commented.

Pressure effects on the structural and electronic properties of ABX 4 scintillating crystals

http://personales.upv.es/~fjmanjon/pms53_711.pdf

Pressure effects on the structural and electronic properties of ABX4 scintillating crystals

This paper deals with structural and morphological developments during flow-induced crystallization of molten isotactic polypropylene (iPP). Several authors have invoked the formation of precursors in the early stages of this process. However, it is not clear whether these precursors can be generated and can crystallize already during flow. We address this issue using X-ray scattering (SAXS and WAXD) with a high image capturing rate during and immediately after a strong shear pulse to the undercooled melt. Eventually, we provide the first in situ evidence of formation of flow-induced precursors (FIPs) of crystallization generated applying shear to a fast crystallizing melt of flexible macromolecules, like iPP. Moreover, it is shown that a rheological classification can be used to define the flow conditions promoting FIPs formation. In fact, when molecular stretch is achieved, we found that shear rate is the parameter dominating the formation of structures during shear. When the shear rate is high enough, ...

http://www.mate.tue.nl/~peters/Papers/2009/BalzanoEA_CrystPrecursors_2009.pdf

Crystallization and Precursors during Fast Short-Term Shear

Tuning the band gap of PbCrO4 through high-pressure: Evidence of wide-to-narrow semiconductor transitions

High pressure Raman scattering study on the phase stability of LuVO4

Pressure-related structural properties of CaCrO4 with zircon-type structure (I41/amd) at ambient pressure were investigated using synchrotron radiation x-ray diffraction in energy-dispersive mode in a diamond anvil cell (DAC) up to 29.1 GPa at room temperature. A sluggish first-order structural phase transition to a scheelite-type phase (I41/a) was observed at 5.7 GPa. The lattice parameters of both phases at different pressures were calculated. The isothermal Birch–Murnaghan equation of state (EOS) was used to fit the data of pressure versus unit cell volume, and the bulk moduli were simulated to be 103.7 ± 0.3 and 125.1 ± 6.2 GPa for the zircon and scheelite phase, respectively.

/pdf/crystal-structural-phase-transition-in-cacro4-under-high-3b3kgla3fi.pdf

Crystal structural phase transition in CaCrO4 under high pressure

We study the entanglement properties of non-Hermitian free fermionic models with translation symmetry using the correlation matrix technique. Our results show that the entanglement entropy has a logarithmic correction to the area law in both one-dimensional and two-dimensional systems. For any one-dimensional one-band system, we prove that each Fermi point of the system contributes exactly 1/2 to the coefficient c of the logarithmic correction. Moreover, this relation between c and Fermi point is verified for more general one-dimensional and two-dimensional cases by numerical calculations and finite-size scaling analysis. In addition, we also study the single-particle and density-density correlation functions.

Entanglement Entropy of Non-Hermitian Free Fermions

We study the entanglement properties of non-Hermitian free fermionic models with translation symmetry using the correlation matrix technique. Our results show that the entanglement entropy has a logarithmic correction to the area law in both one-dimensional and two-dimensional systems. For any one-dimensional one-band system, we prove that each Fermi point of the system contributes exactly 1/2 to the coefficientcof the logarithmic correction. Moreover, this relation betweencand Fermi point is verified for more general one-dimensional and two-dimensional cases by numerical calculations and finite-size scaling analysis. In addition, we also study the single-particle and density-density correlation functions.

Yi-Cong Yu

Papers

Crystal structural phase transition in CaCrO4 under high pressure

Entanglement Entropy of Non-Hermitian Free Fermions

Entanglement entropy of non-Hermitian free fermions.