High-pressure Phase Transformation And Elastic Properties Of Titanium Dioxide,strontium Titanate And Zinc Titanate

Titanium dioxide,strontium titanate,and zinc titanate are typical Ti-bearing inorganic functional materials,which have been widely used in fields such as photocatalysis,photovoltaic cells,electrochemical energy storage,sensors and so on.Researches on titanium dioxide,strontium titanate,and zinc titanate help us to deepen our understanding of their physical and chemical properties,and further improve their performance to meet the needs of different fields.The Ti O₆ octahedron is the structural unit of both titanium dioxide,strontium titanate and zinc titanate.With the development of high-pressure technology,the effect of high pressure on the Ti O₆ octahedron has attracted extensive attention.The properties of titanium dioxide,strontium titanate and zinc titanate are closely related to the arrangement,connectivity,and distortion of the Ti O₆ octahedra,so the effect of high pressure on the Ti O₆ octahedron is the basis for exploring the application value of titanium dioxide,strontium titanate and zinc titanate under extreme conditions.The application of high-pressure technology not only expands the industrial application of titanium dioxide,strontium titanate,and zinc titanate,but also changes their crystal structures and elastic properties under high-pressure conditions.Therefore,it has attracted increasing attention from earth science researchers.The study of crystal structure transformation of titanium dioxide,strontium titanate and zinc titanate under pressure not only enhances our understanding of their behavior under high pressure but also reflects on the behavior of minerals with similar structures under high pressure.This can help us understand the internal composition and material transport of planets.In addition,the changes in elastic properties of titanium dioxide,strontium titanate and zinc titanate induced by pressure can also provide new possible explanations for anomalous variations in velocity structure within planets.This paper focuses on the investigation of the phase stability and elastic properties of rutile-type titanium dioxide（Ti O₂）,strontium titanate（Sr Ti O₃）and zinc titanate（Zn₂Ti O₄）single crystals under high pressure.The following achievements have been obtained:1.Synchrotron X-ray diffraction,Raman scattering,and Brillouin scattering experimental techniques were used to study the phase stability and elastic properties of rutile-type Ti O₂ single crystal under high pressure.The high-pressure phase transition behavior of Ti O₂ single crystal,which is different from the nanocrystalline type,was studied within the pressure range of 0-12.3 GPa at room temperature,and the change of elastic constants with pressure was obtained.It was found that single crystal rutile-type Ti O₂ began to undergo martensitic phase transition at 3.5 GPa,from tetragonal phase to Ti O₂-II phase.The change of elastic constants with pressure at room temperature and within the range of 0-10.3 GPa was also obtained.It was observed that the tilt or deformation of Ti O₆ octahedra caused by the slip of（0 1 1）crystal plane along the[0 1 1]direction during phase transition would lead to anomalous changes in elastic constants at the phase transition pressure point.Using the obtained elastic data of single crystal rutile,the velocity and density of mineral assemblages containing rutile-type Ti O₂ were simulated along the lunar temperature-pressure curve,and the best mineral composition ratio that could fit the typical lunar seismological model was assumed.This achievement provides new insights into the composition and structure of the Moon’s interior.2.The phase stability and elastic properties of Sr Ti O₃ single crystal under high pressure were studied through Raman scattering and Brillouin scattering experimental techniques.The phase behavior and elastic properties of Sr Ti O₃ single crystal were obtained within the pressure range of 0-27.5 GPa at room temperature.At 10.3 GPa,the single crystal Sr Ti O₃ underwent a transition from cubic phase to tetragonal phase,which resulted in the softening of the elastic modulus above 10.3 GPa.In addition,a more accurate Landau potential coefficient was calculated based on the obtained elastic constants.Furthermore,as a structural analogue of the main mineral Ca Si O₃ in the mantle,the anisotropy study of Sr Ti O₃ showed that the tetragonal phase had higher anisotropy compared to the cubic phase,which could help explain the larger transverse wave splitting anisotropy in the mantle.3.The phase stability and elastic properties of Zn₂Ti O₄ single crystal under high pressure were studied using Raman scattering and Brillouin scattering experimental techniques.The phase behavior and elastic properties of Zn₂Ti O₄ single crystal at room temperature and within the pressure range of 0-25.3 GPa were obtained.At a pressure of 19 GPa,Zn₂Ti O₄ single crystal underwent an irreversible phase transition from spinel phase to post-spinel phase.The trend of elastic constants with pressure was obtained,and using the obtained elastic modulus,the changes of transverse sound velocity V_S and longitudinal sound velocity V_P of Zn₂Ti O₄ single crystal with pressure were calculated and compared with other structure spinels.It was found that the sound velocity of single-crystal spinel Zn₂Ti O₄ was much smaller than that of other spinel-structured minerals,suggesting that the bearing of Ti and Zn may reduce the sound velocity of ringwoodite with the same spinel structure,thereby affecting the seismic velocity of the mantle transition zone.