Tilting and Distortion in the Multiferroic Aurivillius Phase Bi6Ti3Fe1.5Mn0.5O18.

Aurivillius structured Bi6Ti3Fe1.5Mn0.5O18 (B6TFMO) has emerged as a rare room temperature multiferroic, exhibiting reversible magnetoelectric switching of ferroelectric domains under cycled magnetic fields. This layered oxide presents exceptional avenues for advancing data storage technologies owing to its distinctive ferroelectric and ferrimagnetic characteristics. Despite its immense potential, a comprehensive understanding of the underlying mechanisms driving multiferroic behavior remains elusive. Herein, we employ atomic resolution electron microscopy to elucidate the interplay of octahedral tilting and atomic-level structural distortions within B6TFMO, associating these phenomena with functional properties. Fundamental electronic features at varying bonding environments within this complex system are scrutinized using electron energy loss spectroscopy (EELS), revealing that the electronic nature of the Ti4+ cations within perovskite BO6 octahedra is influenced by position within the Aurivillius structure. Layer-by-layer EELS analysis shows an ascending crystal field splitting (Δ) trend from outer to center perovskite layers, with an average increase in Δ of 0.13 ± 0.06 eV. Density functional theory calculations, supported by atomic resolution polarization vector mapping of B-site cations, underscore the correlation between the evolving nature of Ti4+ cations, the extent of tetragonal distortion and ferroelectric behavior. Integrated differential phase contrast imaging unveils the position of light oxygen atoms in B6TFMO for the first time, exposing an escalating degree of octahedral tilting toward the center layers, which competes with the magnitude of BO6 tetragonal distortion. The observed octahedral tilting, influenced by B-site cation arrangement, is deemed crucial for juxtaposing magnetic cations and establishing long-range ferrimagnetic order in multiferroic B6TFMO.

Engineering Ferroelectricity and Large Piezoelectricity in h-BN.

Hexagonal boron nitride (h-BN) is a well-known layered van der Waals (vdW) material that exhibits no spontaneous electric polarization due to its centrosymmetric structure. Extensive density functional theory (DFT) calculations are used to demonstrate that doping through the substitution of B by isovalent Al and Ga breaks the inversion symmetry and induces local dipole moments along the c-axis, which promotes a ferroelectric (FE) alignment over antiferroelectric. For doping concentrations below 25%, a "protruded layered" structure in which the dopant atoms protrude out of the planar h-BN layers is energetically more stable than the flat layered structure of pristine h-BN or a wurtzite structure similar to w-AlN. The computed polarization, between 7.227 and 21.117 µC/cm2, depending on dopant concentration and the switching barrier (16.684 and 45.838 meV/atom) for the FE polarization reversal are comparable to that of other well-known FEs. Interestingly, doping of h-BN also induces a large negative piezoelectric response in otherwise nonpiezoelectric h-BN. For example, we compute d33 of -24.214 pC/N for Ga0.125B0.875N, which is about 5 times larger than that of pure w-AlN (5 pC/N), although the computed e33 (-1.164 C/m2) is about 1.6 times lower than that of pure w-AlN (1.462 C/m2). Because of the layered structure, the rather small elastic constant C33 provides the origin of the large d33. Moreover, doping makes h-BN an electric auxetic piezoelectric. We also show that ferroelectricity in doped h-BN may persist down to its trilayer, which indicates high potential for applications in FE nonvolatile memories.

Large piezoelectric response in ferroelectric/multiferroelectric metal oxyhalide MOX2 (M = Ti, V and X = F, Cl and Br) monolayers.

Flexible two-dimensional (2D) piezoelectric materials are promising for applications in wearable electromechanical nano-devices such as sensors, energy harvesters, and actuators. A large piezo-response is required for any practical applications. Based on first-principles calculations, we report that ferroelectric TiOX2 and multiferroelectric VOX2 (X = F, Cl, and Br) monolayers exhibit large in-plane stress (e11) and strain (d11) piezoelectric coefficients. For example, the in-plane piezo-response of TiOBr2 (both e11 = 28.793 × 10-10 C m-1 and d11 = 37.758 pm V-1) is about an order of magnitude larger than that of the widely studied 1H-MoS2 monolayer, and also quite comparable to the giant piezoelectricity of group-IV monochalcogenide monolayers, e.g., SnS. Moreover, the d11 of MOX2 monolayers - ranging from 29.028 pm V-1 to 37.758 pm V-1 - are significantly higher than the d11 or d33 of commonly used 3D piezoelectrics such as w-AlN (d33 = 5.1 pm V-1) and α-quartz (d11 = 2.3 pm V-1). Such a large d11 of MOX2 monolayers originates from low in-plane elastic constants with large e11 due to large Born effective charges (Zij) and atomic sensitivity to an applied strain. Moreover, we show the possibility of opening a new way of controlling piezoelectricity by applying a magnetic field.

Negative Piezoelectric Coefficient in Ferromagnetic 1H-LaBr2 Monolayer.

The discovery of two-dimensional (2D) magnetic materials that have excellent piezoelectric response is promising for nanoscale multifunctional piezoelectric or spintronic devices. Piezoelectricity requires a noncentrosymmetric structure with an electronic band gap, whereas magnetism demands broken time-reversal symmetry. Most of the well-known 2D piezoelectrics, e.g., 1H-MoS2 monolayer, are not magnetic. Being intrinsically magnetic, semiconducting 1H-LaBr2 and 1H-VS2 monolayers can combine magnetism and piezoelectricity. We compare piezoelectric properties of 1H-MoS2, 1H-VS2, and 1H-LaBr2 using density functional theory. The ferromagnetic 1H-LaBr2 and 1H-VS2 monolayers display larger piezoelectric strain coefficients, namely, d 11 = -4.527 pm/V for 1H-LaBr2 and d 11 = 4.104 pm/V for 1H-VS2, compared to 1H-MoS2 (d 11 = 3.706 pm/V). 1H-MoS2 has a larger piezoelectric stress coefficient (e 11 = 370.675 pC/m) than 1H-LaBr2 (e 11 = -94.175 pC/m) and 1H-VS2 (e 11 = 298.100 pC/m). The large d 11 for 1H-LaBr2 originates from the low elastic constants, C 11 = 30.338 N/m and C 12 = 9.534 N/m. The sign of the piezoelectric coefficients for 1H-LaBr2 is negative, and this arises from the negative ionic contribution of e 11, which dominates in 1H-LaBr2, whereas the electronic part of e 11 dominates in 1H-MoS2 and 1H-VS2. We explain the origin of this large ionic contribution of e 11 for 1H-LaBr2 through Born effective charges (Z 11) and the sensitivity of the atomic positions to the strain (du/dη). We observe a sign reversal in the Z 11 values of Mo and S compared to the nominal oxidation states, which makes both the electronic and ionic parts of e 11 positive and results in the high value of e 11. We also show that a change in magnetic order can enhance (reduce) the piezoresponse of 1H-LaBr2 (1H-VS2).

Antibacterial pyrazoles: tackling resistant bacteria.

Bacterial resistance to antibiotics threatens our progress in healthcare, modern medicine, food production and ultimately life expectancy. Antibiotic resistance is a global concern, which spreads rapidly across borders and continents due to rapid travel of people, animals and goods. Derivatives of metabolically stable pyrazole nucleus are known for their wide range of pharmacological properties, including antibacterial activities. This review highlights recent reports of pyrazole derivatives targeting different bacterial strains focusing on the drug-resistant variants. Pyrazole derivatives target different metabolic pathways of both Gram-positive and Gram-negative bacteria.

Large Piezoelectric Response and Ferroelectricity in Li and V/Nb/Ta Co-Doped w-AlN.

Enhancement of piezoelectricity in w-AlN is desired for many devices including resonators for next-generation wireless communication systems, sensors, and vibrational energy harvesters. Based on density functional theory, we show that Li and X (X = V, Nb, and Ta) co-doping in 1Li:1X ratio transforms brittle w-AlN crystal to ductile, along with broadening the compositional freedom for significantly enhanced piezoelectric response, promising them to be good alternatives to expensive Sc. Interestingly, these co-doped w-AlN also show quite large spontaneous electric polarization (e.g., about 1 C/m2 for Li0.125X0.125Al0.75N) with the possibility of ferroelectric polarization switching, opening new possibilities in wurtzite nitrides. An increase in piezoelectric stress constant (e33) with a decrease in elastic constant (C33) results in an enhancement of piezoelectric strain constant (d33), which is desired for improving the performance of bulk acoustic wave (BAW) resonators for high-frequency radio frequency (RF) signals. Also, these co-doped w-AlN are potential lead-free piezoelectric materials for energy harvesting and sensors as they improve the longitudinal electromechanical coupling constant (K332), transverse piezoelectric strain constant (d31), and figure of merit (FOM) for power generation. However, the enhancement in K332 is not as pronounced as that in d33 because co-doping increases dielectric constant. The longitudinal acoustic wave velocity (7.09 km/s) of Li0.1875Ta0.1875Al0.625N is quite comparable to that of commercially used piezoelectric LiNbO3 or LiTaO3 in special cuts (about 5-7 km/s) despite the fact that the acoustic wave velocities, important parameters for designing resonators or sensors, decrease with co-doping or Sc concentration.

Ferroelectricity and Large Piezoelectric Response of AlN/ScN Superlattice.

Based on density functional theory, we investigate the ferroelectric and piezoelectric properties of the AlN/ScN superlattice, consisting of ScN and AlN buckled monolayers alternating along the crystallographic c-direction. We find that the polar wurtzite (w-ScAlN) structure is mechanically and dynamically stable and is more stable than the nonpolar hexagonal flat configuration. We show that ferroelectric polarization switching can be possible for an epitaxially tensile-strained superlattice. Because of the elastic constant C33 softening, together with an increase in e33, the piezoelectric coefficient d33 of the superlattice is doubled compared to that of pure w-AlN. The combined enhancement of Born effective charges ( Z33) and sensitivity of the atomic coordinates to the external strain (∂u3∂η3) is the origin of the large piezoelectric constant e33. Moreover, we show that the epitaxial biaxial tensile strain significantly enhances the piezo-response, so that d33 becomes 7 times larger than that of w-AlN at 4% strain. The tensile strain results in a huge enhancement in e33 by increasing Z33 and ∂u3∂η3 , which boost the piezoelectric.

Switchable Rashba effect by dipole moment switching in an Ag2Te monolayer.

Because of the surface depolarization field, there is a critical thickness for ferroelectricity in ultrathin ferroelectric films, hindering miniaturization of high-density nonvolatile memory storage devices. A controllable Rashba effect by external electric field via switchable dipole moment could be a promising way to control and manipulate the spin degrees of freedom in spintronics. Here, based on first principles calculations, we show that non-planar Ag2Te monolayer, which has been recently predicted to be a topological insulator, possess a switchable out-of-plane electric dipole moment. The switching of the dipole can be realized by the penetration of Te atoms through the hexagonal Ag-plane. Additionally, non-planar Ag2Te shows a giant Rashba spin-splitting ([Formula: see text] eV Å) due to the out-of-plane electric dipole moment. Our tight binding model indicates that the origin of such large [Formula: see text] is the large inversion symmetry breaking term ([Formula: see text] eV), which is one order of magnitude larger in non-planar Ag2Te monolayer compared with other Rashba materials. Interestingly, the Rashba effect can be turned on/off by the phase transition from non-planar to planar structure via Te displacement. Moreover, the spin-texture can be completely reversed because of switchable electric dipole moment. Our work shows a new way to realize ferroelectric-like dipole moment switching and consequently switchable Rashba spin-splitting, which may facilitate a nonvolatile electrical control of the spin degrees of freedom, down to the monolayer thickness, promising potential applications to electrically controlled spintronic devices.

Switchable Polarization in Mn Embedded Graphene.

Graphene, despite its many unique properties, is neither intrinsically polar due to inversion symmetry nor magnetic. However, based on density functional theory, we find that Mn, one of transition metals, embedded in single or double vacancy (Mn@SV and Mn@DV) in a graphene monolayer induces a dipole moment perpendicular to the sheet, which can be switched from up to down by Mn penetration through the graphene. Such switching could be realized by an external stimuli introduced through the tip of a scanning probe microscope, as already utilized in the studies of molecular switches. We estimate the energy barriers for dipole switching, which are found to be 2.60 eV and 0.28 eV for Mn@SV and Mn@DV, respectively. However, by applying biaxial tensile strain, we propose a mechanism for tuning the barrier. We find that 10% biaxial tensile strain, which is already experimentally achievable in graphene-like two-dimensional materials, can significantly reduce the barrier to 0.16 eV in Mn@SV. Moreover, in agreement with previous studies, we find a high magnetic moment of 3 µB for both Mn@SV and Mn@DV, promising the potential of these structures in spintronics as well as in nanoscale electro-mechanical or memory devices.

Therapy Targeting Stem Cell in Patients with Decompensated Cirrhosis of Liver in a Tertiary Treatment Care Center of Bangladesh.

INTRODUCTION: Decompensated cirrhosis is associated with significantly high mortality resulting from hepatic failure, and liver transplantation seems to be the only viable indication for its management. The objective of this study is to assess if granulocyte colony-stimulating factor (G-CSF), a stimulatory of stem cell in vivo, may be of any benefit for patients with decompensated cirrhosis of liver. MATERIALS AND METHODS: Seventeen consecutive patients with decompensated cirrhosis of liver were recruited in this prospective study. They received injection of G-CSF (30 IU) over a period of 6 weeks (12 injections) in addition to standard of care. RESULTS: Patients were followed up at the end of treatment and at 12 weeks of treatment. Treatment was well tolerated, and no significant adverse event was recorded in any patient. Fifteen out of 17 (88%) patients were alive at last follow-up. Although serum bilirubin, albumin, and prothrombin time improved in some patients, statistically significant improvement of Child-Pugh score could not be documented. CONCLUSION: The study establishes the safety of G-CSF therapy in patients with decompensated cirrhosis of liver. Besides, such therapy may also have survival benefit, although long-term follow-up is needed to assess its real utility in clinical perspectives.How to cite this article: Al Mahtab M, Alam SMN, Moben AL, Raihan R, Alam MA, Rahim MA, Uddin MH, Akbar SMF. Therapy Targeting Stem Cell in Patients with Decompensated Cirrhosis of Liver in a Tertiary Treatment Care Center of Bangladesh. Euroasian J Hepato-Gastroenterol 2017;7(1):113-115.

Hepatic Venous Pressure Gradient Measurement in Bangladeshi Cirrhotic Patients: A Correlation with Child's Status, Variceal Size, and Bleeding.

BACKGROUND: Hepatic venous pressure gradient (HVPG) reflects the portal pressure in patients with cirrhotic portal hypertension. The aim of the study was to assess the relation of HVPG to variceal size, Child-Pugh status, and variceal bleeding. MATERIALS AND METHODS: A total of 96 patients with cirrhosis of liver were enrolled prospectively and each patient's HVPG level was measured via the transfemoral route. Clinical and biochemical evaluation and upper gastrointestinal (GI) endoscopy were done in each subject. Severity of cirrhosis was assessed by Child's status. RESULTS: The mean HVPG was higher in patients with Child's B and C (14.10 ± 7.56 and 13.64 ± 7.17 mm Hg respectively) compared with those of Child's A (10.15 ± 5.63 mm Hg). The levels of HVPG differed significantly between Child's classes A and B (p = 0.011) and Child's A and C (p = 0.041). The mean HVPG was also higher in bleeders compared with nonbleeders with large varices (17.7 ± 5.5 vs 14.9 ± 4.7 mmHg respectively; p = 0.006). CONCLUSION: Hepatic venous pressure gradient seems to be important to assess the severity of liver cirrhosis.How to cite this article: Al Mahtab M, Noor E Alam SM, Rahim MA, Alam MA, Khondaker FA, Moben AL, Mohsena M, Akbar SMF. Hepatic Venous Pressure Gradient Measurement in Bangladeshi Cirrhotic Patients: A Correlation with Child's Status, Variceal Size, and Bleeding. Euroasian J Hepato-Gastroenterol 2017;7(2):142-145.

Switchable polarization in an unzipped graphene oxide monolayer.

Ferroelectricity in low-dimensional oxide materials is generally suppressed at the scale of a few nanometers, and has attracted considerable attention from both fundamental and technological aspects. Graphene is one of the thinnest materials (one atom thick). Therefore, engineering switchable polarization in non-polar pristine graphene could potentially lead to two-dimensional (2D) ferroelectric materials. In the present study, based on density functional theory, we show that an unzipped graphene oxide (UGO) monolayer can exhibit switchable polarization due to its foldable bonds between the oxygen atom and two carbon atoms underneath the oxygen. We find that a free standing UGO monolayer exhibits antiferroelectric switchable polarization. A UGO monolayer can be obtained as an intermediate product during the chemical exfoliation process of graphene. Interestingly, despite its dimensionality, our estimated polarization in a UGO monolayer is comparable to that in bulk ferroelectric materials (e.g., ferroelectric polymers). Our calculations could help realize antiferroelectric switchable polarization in 2D materials, which could find various potential applications in nanoscale devices such as sensors, actuators, and capacitors with high energy-storage density.

Dipolar polarization and piezoelectricity of a hexagonal boron nitride sheet decorated with hydrogen and fluorine.

In contrast to graphene, a hexagonal boron nitride (h-BN) monolayer is piezoelectric because it is non-centrosymmetric. However, h-BN shows neither in-plane nor out-of-plane dipole moments due to its three-fold symmetry on the plane and the fact that it is completely flat. Here, we show that the controlled adsorption of hydrogen and/or fluorine atoms on both sides of a pristine h-BN sheet induces flatness distortion in a chair form and an out-of plane dipole moment. In contrast, a boat form has no out-of-plane dipole moment due to the alternating boron and nitrogen positions normal to the plane. Consequently, the chair form of surface-modified h-BN shows both in-plane and out-of-plane piezoelectric responses; while pristine h-BN and the boat form of decorated h-BN have only in-plane piezoelectric responses. These in-plane and out-of-plane piezoelectric responses of the modified h-BN are comparable to those in known three-dimensional piezoelectric materials. Such an engineered piezoelectric two-dimensional boron nitride monolayer can be a candidate material for various nano-electromechanical applications.