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1. Structural and mechanical properties of nanocrystalline Ga ₂ O ₃ films made by pulsed laser deposition onto transparent quartz substrates

   https://doi.org/10.1088/2632-959X/abf3d3  

   Zade, Vishal; Makeswaran, Nanthakishore; Boyce, Brad L.; Paraguay-Delgado, Francisco; Ramana, C. V. (April 2021, Nano Express)

   Abstract This work reports on the correlation between structure, surface/interface morphology and mechanical properties of pulsed laser deposited (PLD)β-Ga₂O₃films on transparent quartz substrates. By varying the deposition temperature in the range of 25 °C–700 °C, ∼200 nm thick Ga₂O₃films with variable microstructure and amorphous-to-nanocrystalline nature were produced onto quartz substrates by PLD. The Ga₂O₃films deposited at room temperature were amorphous; nanocrystalline Ga₂O₃films were realized at 700 °C. The interface microstructure is characterized with a typical nano-columnar morphology while the surface exhibits the uniform granular morphology. Corroborating with structure and surface/interface morphology, and with increasing deposition temperature, tunable mechanical properties were seen in PLD Ga₂O₃films. At 700 °C, for nanocrystalline Ga₂O₃films, the dense grain packing reduces the elastic modulus E_rwhile improving the hardness. The improved crystallinity at elevated temperatures coupled with nanocrystallinity, theβ-phase stabilization is accounted for the observed enhancement in the mechanical properties of PLD Ga₂O₃films. The structure-morphology-mechanical property correlation in nanocrystalline PLDβ-Ga₂O₃films deposited on quartz substrates is discussed in detail. 

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2. A New High-Pressure Phase Transition in Natural Gedrite

   https://doi.org/10.3390/cryst9100521  

   Yong, Tommy; Bina, Craig R.; Finkelstein, Gregory J.; Zhang, Dongzhou; Dera, Przemyslaw (October 2019, Crystals)

   High-pressure diamond-anvil cell synchrotron X-ray diffraction experiments were conducted on single-crystal samples of natural orthoamphibole; gedrite; with composition; (K0.002Na0.394)(Mg2)(Mg1.637Fe2.245Mn0.004Ca0.022Cr0.003Na0.037Al1.052)(Si6.517Al1.483)O22(OH)2. The samples were compressed at 298 K up to a maximum pressure of 27(1) GPa. In this pressure regime, we observed a displacive phase transition between 15.1(7) and 21(1) GPa from the orthorhombic Pnma phase to a new structure with space group P21/m; which is different from the familiar P21/m structure of cummingtonite and retains the (+, +, −, −) I-beam stacking sequence of the orthorhombic structure. The unit cell parameters for the new phase at 21(1) GPa are a = 17.514(3), b = 17.077(1), c = 4.9907(2) Å and β = 92.882(6)°. The high-pressure P21/m phase is the first amphibole structure to show the existence of four crystallographically distinct silicate double chains. The orthorhombic to monoclinic phase transition is characterized by an increase in the degree of kinking of the double silicate chains and is analogous to displacive phase changes recently reported in orthopyroxenes, highlighting the parallel structural relations and phase transformation behavior of orthorhombic single- and double-chain silicates. 

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3. Direct observation of a magnetic-field-induced Wigner crystal

   https://doi.org/10.1038/s41586-024-07212-7  

   Tsui, Yen-Chen; He, Minhao; Hu, Yuwen; Lake, Ethan; Wang, Taige; Watanabe, Kenji; Taniguchi, Takashi; Zaletel, Michael P; Yazdani, Ali (April 2024, Nature)

   Wigner predicted that when the Coulomb interactions between electrons become much stronger than their kinetic energy, electrons crystallize into a closely packed lattice1. A variety of two-dimensional systems have shown evidence for Wigner crystals2,3,4,5,6,7,8,9,10,11 (WCs). However, a spontaneously formed classical or quantum WC has never been directly visualized. Neither the identification of the WC symmetry nor direct investigation of its melting has been accomplished. Here we use high-resolution scanning tunnelling microscopy measurements to directly image a magnetic-field-induced electron WC in Bernal-stacked bilayer graphene and examine its structural properties as a function of electron density, magnetic field and temperature. At high fields and the lowest temperature, we observe a triangular lattice electron WC in the lowest Landau level. The WC possesses the expected lattice constant and is robust between filling factor ν ≈ 0.13 and ν ≈ 0.38 except near fillings where it competes with fractional quantum Hall states. Increasing the density or temperature results in the melting of the WC into a liquid phase that is isotropic but has a modulated structure characterized by the Bragg wavevector of the WC. At low magnetic fields, the WC unexpectedly transitions into an anisotropic stripe phase, which has been commonly anticipated to form in higher Landau levels. Analysis of individual lattice sites shows signatures that may be related to the quantum zero-point motion of electrons in the WC lattice. 

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4. A Pressure‐Induced Inverse Order–Disorder Transition in Double Perovskites

   https://doi.org/10.1002/anie.202001922  

   Deng, Zheng; Kang, Chang‐Jong; Croft, Mark; Li, Wenmin; Shen, Xi; Zhao, Jianfa; Yu, Richeng; Jin, Changqing; Kotliar, Gabriel; Liu, Sizhan; et al (April 2020, Angewandte Chemie International Edition)

   Abstract Given the consensus that pressure improves cation ordering in most of known materials, a discovery of pressure‐induced disordering could require recognition of an order–disorder transition in solid‐state physics/chemistry and geophysics. Double perovskites Y₂CoIrO₆and Y₂CoRuO₆polymorphs synthesized at 0, 6, and 15 GPa show B‐site ordering, partial ordering, and disordering, respectively, accompanied by lattice compression and crystal structure alteration from monoclinic to orthorhombic symmetry. Correspondingly, the long‐range ferrimagnetic ordering in the B‐site ordered samples are gradually overwhelmed by B‐site disorder. Theoretical calculations suggest that unusual unit‐cell compressions under external pressures unexpectedly stabilize the disordered phases of Y₂CoIrO₆and Y₂CoRuO₆. 

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5. The precipitation, growth and stability of mercury sulfide nanoparticles formed in the presence of marine dissolved organic matter

   https://doi.org/10.1039/c7em00593h  

   Mazrui, Nashaat M.; Seelen, Emily; King'ondu, Cecil K.; Thota, Sravan; Awino, Joseph; Rouge, Jessica; Zhao, Jing; Mason, Robert P. (January 2018, Environmental Science: Processes & Impacts)

   The methylation of mercury is known to depend on the chemical forms of mercury (Hg) present in the environment and the methylating bacterial activity. In sulfidic sediments, under conditions of supersaturation with respect to metacinnabar, recent research has shown that mercury precipitates as β-HgS(s) nanoparticles (β-HgS(s) nano ). Few studies have examined the precipitation of β-HgS(s) nano in the presence of marine dissolved organic matter (DOM). In this work, we used dynamic light scattering (DLS) coupled with UV-Vis spectroscopy and transmission electron microscopy (TEM) to investigate the formation and fate of β-HgS(s) nano formed in association with marine DOM extracted from the east and west of Long Island Sound, and at the shelf break of the North Atlantic Ocean, as well as with low molecular weight thiols. We found that while the β-HgS(s) nano formed in the presence of oceanic DOM doubled in size after 5 weeks, those forming in solutions with coastal DOM did not grow over time. In addition, when the Hg II  : DOM ratio was varied, β-HgS(s) nano only rapidly aggregated at high ratios (>41 μmol Hg II per mg C) where the concentration of thiol groups was determined to be substantially low relative to Hg II . This suggests that functional groups other than thiols could be involved in the stabilization of β-HgS(s) nano . Furthermore, we showed that β-HgS(s) nano forming under anoxic conditions remained stable and could therefore persist in the environment sufficiently to impact the methylation potential. Exposure of β-HgS(s) nano to sunlit and oxic environments, however, caused rapid aggregation and sedimentation of the nanoparticles, suggesting that photo-induced changes or oxidation of organic matter adsorbed on the surface of β-HgS(s) nano affected their stability in surface waters. 

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