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1. Creation, stabilization, and investigation at ambient pressure of pressure-induced superconductivity in Bi _0.5 Sb _1.5 Te ₃

   https://doi.org/10.1073/pnas.2423102122  

   Deng, Liangzi; Wang, Busheng; Halbert, Clayton; Schulze, Daniel J; Gooch, Melissa; Bontke, Trevor; Kuo, Ting-Wei; Shi, Xin; Song, Shaowei; Salke, Nilesh; et al (February 2025, Proceedings of the National Academy of Sciences)

   In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T_cs) across various systems have been achieved under high pressure, the primary challenge for higher T_cshould no longer solely be to increase T_cunder extreme conditions but also to reduce, or ideally eliminate, the need for applied pressure in retaining pressure-induced or -enhanced superconductivity. The topological semiconductor Bi_0.5Sb_1.5Te₃(BST) was chosen to demonstrate our approach to addressing this challenge and exploring its intriguing physics. Under pressures up to ~50 GPa, three superconducting phases (BST-I, -II, and -III) were observed. A superconducting phase in BST-I appears at ~4 GPa, without a structural transition, suggesting the possible topological nature of this phase. Using the pressure-quench protocol (PQP) recently developed by us, we successfully retained this pressure-induced phase at ambient pressure and revealed the bulk nature of the state. Significantly, this demonstrates recovery of a pressure-quenched sample from a diamond anvil cell at room temperature with the pressure-induced phase retained at ambient pressure. Other superconducting phases were retained in BST-II and -III at ambient pressure and subjected to thermal and temporal stability testing. Superconductivity was also found in BST with T_cup to 10.2 K, the record for this compound series. While PQP maintains superconducting phases in BST at ambient pressure, both depressurization and PQP enhance its T_c, possibly due to microstructures formed during these processes, offering an added avenue to raise T_c. These findings are supported by our density-functional theory calculations. 

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2. Predicted hot superconductivity in LaSc ₂ H ₂₄ under pressure

   https://doi.org/10.1073/pnas.2401840121  

   He, Xin-Ling; Zhao, Wenbo; Xie, Yu; Hermann, Andreas; Hemley, Russell J; Liu, Hanyu; Ma, Yanming (June 2024, Proceedings of the National Academy of Sciences)

   The recent theory-driven discovery of a class of clathrate hydrides (e.g., CaH₆, YH₆, YH₉, and LaH₁₀) with superconducting critical temperatures (T_c) well above 200 K has opened the prospects for “hot” superconductivity above room temperature under pressure. Recent efforts focus on the search for superconductors among ternary hydrides that accommodate more diverse material types and configurations compared to binary hydrides. Through extensive computational searches, we report the prediction of a unique class of thermodynamically stable clathrate hydrides structures consisting of two previously unreported H₂₄and H₃₀hydrogen clathrate cages at megabar pressures. Among these phases, LaSc₂H₂₄shows potential hot superconductivity at the thermodynamically stable pressure range of 167 to 300 GPa, with calculatedT_cs up to 331 K at 250 GPa and 316 K at 167 GPa when the important effects of anharmonicity are included. The very high critical temperatures are attributed to an unusually large hydrogen-derived density of states at the Fermi level arising from the newly reported peculiar H₃₀as well as H₂₄cages in the structure. Our predicted introduction of Sc in the La–H system is expected to facilitate future design and realization of hot superconductors in ternary clathrate superhydrides. 

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3. A Novel High‐Pressure Tin Oxynitride Sn ₂ N ₂ O

   https://doi.org/10.1002/chem.201904529  

   Bhat, Shrikant; Wiehl, Leonore; Haseen, Shariq; Kroll, Peter; Glazyrin, Konstantin; Gollé‐Leidreiter, Philipp; Kolb, Ute; Farla, Robert; Tseng, Jo‐Chi; Ionescu, Emanuel; et al (January 2020, Chemistry – A European Journal)
4. High-Pressure Polymorphism in Silver Ferrite Delafossite, AgFeO ₂

   https://doi.org/10.1021/acs.inorgchem.3c04631  

   Manganaro, Nicholas S; Ambos, Scott D; DeCapua, Matthew; Thiel, Scott D; Mitchell, Wyatt E; Liu, Zhenxian; Zhang, Dongzhou; Nguyen, Phuong_Q H; Lavina, Barbara; Alp, Esen Ercan; et al (May 2024, Inorganic Chemistry)

   The delafossites are a class of layered metal oxides that are notable for being able to exhibit optical transparency alongside an in-plane electrical conductivity, making them promising platforms for the development of transparent conductive oxides. Pressure-induced polymorphism offers a direct method for altering the electrical and optical properties in this class, and although the copper delafossites have been studied extensively under pressure, the silver delafossites remain only partially studied. We report two new high-pressure polymorphs of silver ferrite delafossite, AgFeO2, that are stabilized above ∼6 and ∼14 GPa. In situ X-ray diffraction and vibrational spectroscopy measurements are used to examine the structural changes across the two phase transitions. The high-pressure structure between 6 and 14 GPa is assigned as a monoclinic C2/c structure that is analogous to the high-pressure phase reported for AgGaO2. Nuclear resonant forward scattering reveals no change in the spin state or valence state at the Fe3+ site up to 15.3(5) GPa. 

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5. Pressure-induced metallization and 3d-like behavior in TcS ₂

   https://doi.org/10.1039/d2cc01676a  

   Sayre, Dean; Siska, Emily; Smith, G. Alexander; Chang, Nicholas; Park, Changyong; Poineau, Frederic; Schwartz, Craig P.; Lawler, Keith V.; Salamat, Ashkan (June 2022, Chemical Communications)

   TcS 2 undergoes a charge transfer insulator to metal transition above 28 GPa. Laser annealing reveals a kinetically hindered high pressure arsenopyrite phase that is recoverable to ambient. The new phase is similar to the Mn-dichalcogenides rather than the expected Re-dichalcogenides and involves the formation of S–S and Tc–Tc bonds. 

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