Thermodynamic, electronic, and optical properties of ultra-wide bandgap zirconium-doped tin dioxide from a DFT perspective.

The effects of zirconium doping on the thermodynamic, electronic, and optical properties of tin dioxide are investigated by using density functional theory calculations combined with the cluster expansion method. In the whole composition range, the formation enthalpies of all structures are positive, indicating that SnO2-ZrO2 is an immiscible system and the ZrSnO2 alloy has a tendency of phase separation at low temperature. The x-T phase diagram of ZrSnO2 ternary alloy shows that the critical temperature is 979 K, which means that when the growth temperature of ZrSnO2 crystal is higher than the critical temperature, it is possible to realize the full-component solid solution. The bandgaps of ZrxSn1-xO2 alloys (0 ≤ x ≤ 1) are direct and increase as the Zr composition increases. Zr doping can tune the bandgap of SnO2 from the ultraviolet-B region to the deep ultraviolet region, and has a strong optical response to deep ultraviolet light. The projected density of states and band offsets clearly reveal the reason for the increase of bandgap, which provides useful information to design relevant optoelectronic devices such as quantum wells and solar-blind deep ultraviolet photodetectors.

Transmutation Engineering Makes a Large Class of Stable and Exfoliable A3BX2 Compounds with Exceptional High Magnetic Critical Temperatures and Exotic Electronic Properties.

We establish a robust protocol for materials innovation based on our proposed transmutation engineering strategy combined with combinatorial chemistry and hierarchical high-throughput screening to make a large class of layered 2D A3BX2 materials. After several rounds of efficient screening, 60 types of easily exfoliable and highly stable A3BX2 monolayers have been obtained. Excitingly, four representative monolayers (ferromagnetic Fe3SiS2 and Fe3GeS2, antiferromagnetic Mn3PbTe2 and Co3GeSe2) demonstrate quite high magnetic critical temperatures of 600 (TC), 630 (TC), 770 (TN), and 510 K (TN), respectively. Through electronic fingerprint identification, the magnetic exchange mechanism is fundamentally unveiled at the atomic level in combination with a local chemical topology environment and crystal/exchange field. Furthermore, two simple and effective unified descriptors are proposed to perfectly explain the origin of magnetic strain regulation. Some intriguing materials (featuring double Dirac cones, node-loops, and ultrahigh Fermi velocities) are expected to be used in high-speed and low-dissipation nanodevices. This material family forms a dataset, which establishes a platform to discover and explore unexpected physicochemcial properties and develop promising applications under different circumstances. The chemical trends of diverse properties for this class of materials are revealed, which offers guiding insights for the development of spintronics and nanoelectronics with the target of exploiting both spin and charge degrees of freedom directed functional materials design and screening.

Effective modulation of the exotic properties of two-dimensional multifunctional TM2@g-C4N3 monolayers via transition metal permutation and biaxial strain.

The exotic physicochemical properties of TM atom (3d, 4d, and 5d) embedded g-C4N3 as a novel class of 2D monolayers were systematically investigated through hierarchical high-throughput screening combined with spin-polarized first-principles calculations. After several rounds of efficient screening, 18 types of TM2@g-C4N3 monolayers with a TM atom embedded g-C4N3 substrate in large cavities on both sides in asymmetrical mode have been obtained. The effects of transition metal permutation and biaxial strain on the magnetic, electronic, and optical properties of TM2@g-C4N3 monolayers were comprehensively and deeply analyzed. By anchoring different TM atoms, various magnetic states including ferromagnetism (FM), antiferromagnetism (AFM), and nonmagnetism (NM) can be obtained. The Curie temperatures of Co2@ and Zr2@g-C4N3 are substantially improved up to 305 K and 245 K by applying -8% and -12% compression strains, respectively. This makes them promising candidates for low-dimensional spintronic device applications at or close to room temperature. Additionally, rich electronic states (metal, semiconductor, and half-metal) can be realized through biaxial strains or diverse metal permutations. Interestingly, the Zr2@g-C4N3 monolayer undergoes a transition of FM semiconductor → FM half-metal → AFM metal under biaxial strains from -12% to 10%. Notably, the embedding of TM atoms dramatically enhances visible light absorption compared to bare g-C4N3. Excitingly, the power conversion efficiency of the Pt2@g-C4N3/BN heterojunction can be as high as 20.20%, which has great potential in solar cell applications. This large class of 2D multifunctional materials provides a candidate platform to develop promising applications under different circumstances and is expected to be prepared in the future.

Inter-Conversion between Different Compounds of Ternary Cs-Pb-Br System.

The perovskite CsPbBr3 attracts great attention due to its potential in optoelectronics. However, stability remains a major obstacle to achieving its effecting application. In this work, we prepared CsPbBr3 solids through a simple reaction and investigated reversible conversion between CsPbBr3, Cs4PbBr6, and CsPb2Br5. We found that CsPbBr3 can be respectively converted to Cs4PbBr6 or CsPb2Br5 by reacting with CsBr or PbBr2. Thermodynamic analysis demonstrated that the chemical reactions above were exothermic and occurred spontaneously. Moreover, the formed Cs4PbBr6 could be converted to CsPbBr3 reversely, and then progressively converted to Cs-deficient CsPb2Br5 by extraction of CsBr with water. The CsPb2Br5 was converted to CsPbBr3 reversely under thermal annealing at 400 °C. The thermodynamic processes of these conversions between the three compounds above were clarified. Our findings regarding the conversions not only provide a new method for controlled synthesis of the ternary Cs-Pb-Br materials but also clarify the underlying mechanism for the instability of perovskites CsPbBr3.