Pressurizing the van der Waals magnet FeOCl at low temperatures: Phase transitions and structural evolution

Magnetic order is frustrated on the orthorhombic lattice of van der Waals layered FeOCl. Antiferromagnetic (AFM) order is attained at ambient pressure upon cooling through $T_N$=81 K, due to an accompanying monoclinic lattice distortion lifting the magnetic frustration. Within the paramagnetic state at 293 K, an incommensurate structural modulation appears above a critical pressure of $p_c$≈15 GPa, while orthorhombic symmetry is retained. This modulation is related to an optimization of the packing of chlorine atoms within the van der Waals gap. Here, we report four new phases in the pressure-temperature (p,T) phase diagram of FeOCl below room temperature. High-pressure–low-temperature single-crystal x-ray diffraction (SXRD) up to 37.8 GPa reveals that, at 100 K, the AFM transition occurs at p=7.3±1.3 GPa. The pressure coefficient of $ΔT_N/Δp=2$.13 K/GPa explains that FeOCl remains paramagnetic up to the highest measured pressure of 33.3 GPa at 293 K. At 6 and 100 K, the structural modulation appears around $p_c$≈15 GPa within the AFM ordered phase with monoclinic symmetry. The monoclinic and triclinic lattice distortions increase with pressure up to $γ$=90.64(1)∘, much larger than the maximum value of 90.1∘, that can be reached upon cooling at ambient pressure. The structural evolution provides the geometrical basis for the increase with the pressure of direct 3d−3d exchange and superexchange interactions. It is proposed, that a strong monoclinic lattice distortion may be of importance for understanding the properties of single-layer FeOCl materials

Single-crystal-to-single-crystal phase transitions of commensurately modulated sodium saccharinate 1.875-hydrate

This work reports reversible, single-crystal-to-single-crystal phase transitions of commensurately modulated sodium saccharinate 1.875-hydrate [Na(sac)(15/8)H$_2$O]. The phases were studied in the temperature range 298 to 20 K. They exhibit complex disordered states. An unusual reentrant disorder has been discovered upon cooling through a phase transition at 120 K. The disordered region involves three sodium cations, four water molecules and one saccharinate anion. At room temperature, the structure is an eightfold superstructure that can be described by the superspace group C$_2$/c(0σ$_2$0)s0 with q = (0, 3/4, 0). It demonstrates maximum disorder with the disordered chemical entities having slightly different but close to 0.50:0.50 disorder component ratios. Upon cooling, the crystal tends to an ordered state, smoothly reaching a unified disorder component ratio of around 0.90:0.10 for each of the entities. Between 130 and 120 K a phase transition occurs involving a sudden increase of the disorder towards the disorder component ratio 0.65:0.35. Meanwhile, the space group and general organization of the structure are retained. Between 60 and 40 K there is another phase transition leading to a twinned triclinic phase. After heating the crystal back to room temperature its structure is the same as before cooling, indicating a complete reversibility of the phase transitions

Charge density wave and lock-in transitions of CuV2S4\mathrm{CuV_2S_4}

The three-dimensional charge density wave (CDW) compound $\mathrm{CuV_2S_4}$ is known to undergo phase transitions at ∼91 and ∼50K. Employing single-crystal x-ray diffraction on an annealed crystal, we confirm the formation of an incommensurate CDW at $T_{CDW} ≈$ 91K, and we establish the nature of the transition at $T_{lock-in} ≈$50K as a lock-in transition toward a threefold superstructure. As-grown crystals develop the same incommensurate CDW as the annealed crystal does, but they fail to go through the lock-in transition. Instead, the length of the modulation wave vector continues to decrease down to low temperatures in as-grown crystals. These findings are corroborated by distinct temperature dependencies of the electrical resistivity, magnetic susceptibility, and specific heat measured on as-grown and annealed crystals. A superspace model for the crystal structure of the incommensurate CDW suggests that the formation of extended vanadium clusters is at the origin of the CDW. In the lock-in phase, short and long V-V distances persist, but clusters now percolate the entire crystal. The lowering toward orthorhombic symmetry appears to be responsible for the precise pattern of short and long V-V distances. However, the orthorhombic lattice distortion is nearly zero for the annealed crystal, while it is visible for the as-grown material, again suggesting the role of lattice defects in the latter

Coupling between Charge Density Wave Ordering and Magnetism in Ho2_2Ir3_3Si5_5

Ho$_2$Ir$_3$Si$_5$ belongs to the family of three-dimensional (3D) R$_2$Ir$_3$Si$_5$ (R = Lu, Er, Ho) compounds that exhibit a first-order, charge-density-wave (CDW) phase transition, where there is a strong orthorhombic-to-triclinic distortion of the lattice accompanied by superlattice reflections. The analysis by single-crystal X-ray diffraction (SXRD) has revealed that the Ir–Ir zigzag chains along c are responsible for the CDW in all three compounds. The replacement of the rare earth element from nonmagnetic Lu to magnetic Er or Ho lowers T$_{CDW}$, where T$_{CDWLu}$ = 200 K, T$_{CDWEr}$ = 150 K, and T$_{CDWHo}$ = 90 K. Out of the three compounds, Ho$_2$Ir$_3$Si$_5$ is the only system where second-order superlattice reflections could be observed, indicative of an anharmonic shape of the modulation wave. The CDW transition is observed as anomalies in the temperature dependencies of the specific heat, electrical conductivity, and magnetic susceptibility, which includes a large hysteresis of 90 to 130 K for all measured properties, thus corroborating the SXRD measurements. Similar to previously reported Er$_2$Ir$_3$Si$_5$, there appears to be a coupling between CDW and magnetism such that the Ho$^{3+}$ magnetic moments are influenced by the CDW transition, even in the paramagnetic state. Moreover, earlier investigations on polycrystalline material revealed antiferromagnetic (AFM) ordering at T$_N$ = 5.1 K, whereas AFM order is suppressed and only the CDW is present down to at least 0.1 K in our highly ordered single crystal. First-principles calculations predict Ho$_2$Ir$_3$Si$_5$ to be a metal with coexisting electron and hole pockets at the Fermi level. The Ho and Ir atoms have spherically symmetric metallic-type charge density distributions that are prone to CDW distortion. Phonon calculations affirm that the Ir atoms are primarily responsible for the CDW distortion, which is in agreement with the experiment

miR-579-3p Controls Hepatocellular Carcinoma Formation by Regulating the Phosphoinositide 3-Kinase-Protein Kinase B Pathway in Chronically Inflamed Liver.

Chronic liver inflammation causes continuous liver damage with progressive liver fibrosis and cirrhosis, which may eventually lead to hepatocellular carcinoma (HCC). Whereas the 10-year incidence for HCC in patients with cirrhosis is approximately 20%, many of these patients remain tumor free for their entire lives. Clarifying the mechanisms that define the various outcomes of chronic liver inflammation is a key aspect in HCC research. In addition to a wide variety of contributing factors, microRNAs (miRNAs) have also been shown to be engaged in promoting liver cancer. Therefore, we wanted to characterize miRNAs that are involved in the development of HCC, and we designed a longitudinal study with formalin-fixed and paraffin-embedded liver biopsy samples from several pathology institutes from Switzerland. We examined the miRNA expression by nCounterNanostring technology in matched nontumoral liver tissue from patients developing HCC (n = 23) before and after HCC formation in the same patient. Patients with cirrhosis (n = 26) remaining tumor free within a similar time frame served as a control cohort. Comparison of the two cohorts revealed that liver tissue from patients developing HCC displayed a down-regulation of miR-579-3p as an early step in HCC development, which was further confirmed in a validation cohort. Correlation with messenger RNA expression profiles further revealed that miR-579-3p directly attenuated phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) expression and consequently protein kinase B (AKT) and phosphorylated AKT. In vitro experiments and the use of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology confirmed that miR-579-3p controlled cell proliferation and cell migration of liver cancer cell lines. Conclusion: Liver tissues from patients developing HCC revealed changes in miRNA expression. miR-579-3p was identified as a novel tumor suppressor regulating phosphoinositide 3-kinase-AKT signaling at the early stages of HCC development

Immediate Formation/Precipitation of Icosahedrally Structured Iron-Molybdenum Mixed Oxides from Solutions Upon Mixing Simple Iron(III) and Molybdate Salts

Kuepper K, Neumann M, Al-Karawi AJM, et al. Immediate Formation/Precipitation of Icosahedrally Structured Iron-Molybdenum Mixed Oxides from Solutions Upon Mixing Simple Iron(III) and Molybdate Salts. Journal of Cluster Science. 2014;25(1):301-311.The present investigation refers to nanostructured mixed metal oxides-more specifically to iron-molybdenum oxides most simply obtained by addition of iron(III) chloride to an aqueous solution of sodium molybdate acidified with acetic acid. The immediately obtained yellow non-crystalline solid consists of highly symmetrical icosahedral {Mo72Fe30} motifs which is proven by IR, Raman, Fe-57 Mossbauer and XP spectra. This remarkable result is obtained in spite of the immediate precipitation of the mentioned compound and even from an inhomogeneous mixture of the educts. This again proves the high formation tendency of spherical clusters. The procedure offers in principle the option to encapsulate species present in solution