Enhanced photocatalytic hydrogen production on GaN–ZnO oxynitride by introduction of strain-induced nitrogen vacancy complexes

High‐pressure torsion of SiO2 quartz sand: Phase transformation, optical properties, and significance in geology

“…It should be noted that XPS spectra, as shown in Figure 6C,D, provide no clear evidence for oxygen vacancy generation probably because the concentration of vacancies is below the detection limits of XPS. It is then concluded that HPT processing can induce oxygen vacancies in SiO 2 in good agreement with the earlier reports on the formation of vacancies in the HPT‐processed TiO 2 , 11 ZnO, 12 TiO 2 ‐ZnO, 13 Al 2 O 3 , 14,15 BaTiO 3 16 and ZrO 2 , 17 LiTaO 3 18 and GaZnON 22 . The formation of vacancies by HPT processing is usually attributed to the effect of strain on continuous formation of vacancies and to the effect of pressure on suppressing the migration and annihilation of vacancies 3,70–72 .…”

“…Since HPT processing at room temperature (~300 K) was not so effective to make significant changes in SiO 2 , the experiments were mainly focused on the sample processed at 723 K. As shown in Figure 1B, the color of samples processed at high temperature changes from white to light brown after HPT processing, but the sample processed at room temperature still shows white color. The change of the color of sample after HPT processing suggests a transition in the light absorbance edge, which has already been proved in the authors' previous works 17,22 …”

“…Severe plastic deformation via the high‐pressure torsion (HPT) method has been utilized for decades for processing different metallic materials to achieve ultrafine grains, 1,2 large density of lattice defects, 3,4 metastable phases 5,6 and exceptional structural and functional properties 7,8 . The HPT method is applicable not only to metallic materials 9,10 but also to brittle and hard nonmetallic materials such as oxides (TiO 2 , 11 ZnO, 12 TiO 2 ‐ZnO, 13 Al 2 O 3 , 14,15 BaTiO 3 , 16 ZrO 2 , 17 LiTaO 3 18 ), nitrides, 19 carbides 20,21 and oxynitrides 22 . So far, the HPT method has been utilized for processing nonmetallic materials with two main motivations: (a) fundamental investigation of strain effect on structural and microstructural changes such as phase transformation and oxygen vacancy formation 11–14 ; (b) developing new functional materials with enhanced dielectricity, 16 electrocatalysis, 23 and photocatalysis 11–14,17,22 …”

High-Pressure Torsion for Synthesis of High-Entropy Alloys

“…Besides the popular application of the method to produce UFG materials [8][9][10][11], it has also been used to control phase transformations [12][13][14], consolidate powders [15][16][17] and conduct mechanical alloying [18][19][20]. Moreover, the application of HPT is no longer limited to metallic materials-the method has been applied to nonmetallic materials such as carbon polymorphs [21,22], silicon polymorphs [21,23], oxides [24,25], oxynitrides [26] and glasses [27,28] as well. Compared to other SPD methods such as equal-channel angular pressing (ECAP) [29], accumulative roll-bonding (ARB) [30] and twist extrusion (TE) [31], HPT has the unique capability of introducing extremely large strains in almost any kind of materials, including hard and brittle ones, due to its high processing pressure [1][2][3][4].…”

Gradient bandgap narrowing in severely deformed ZnO nanoparticles

“…[11] for review). In addition to grain refinement and phase transformations, formation of oxygen vacancies during HPT processing has been observed in a range of oxides nanoparticles including BaTiO 3 [13], TiO 2 [14], ZnO [15], Al 2 O 3 [16], Y 2 O 3 [17], and GaN-ZnO [18].…”