High Pressure Structure And Superconducting Transition Temperature Of Ternary Cerium Hydrogen Compounds

Since 1911,Onnes discovered the phenomenon that the resistance value of mercury suddenly drops to zero when the temperature is reduced to 4.2 K,superconductivity has been the research hotspot of wide attention for more than one hundred years until now.In 2004,Ashcroft proposed that non-hydrogen elements in hydrogen-rich compounds interact with hydrogen elements and thus chemically prepress the hydrogen’s daughter lattice,making it easier to metallize and potentially serve as high-temperature superconductors.According to the BCS theory,the superconducting transition temperature of a material is directly proportional to its Debye temperature,which in turn is inversely proportional to the mass of the material.It can be inferred that hydrogen,the lightest element in the world,is likely to have a high superconducting transition temperature.For these reasons,hydrides superconductors have become the focus of scientists.At the beginning,the focus of people’s work was mainly focused on binary hydrides,various potential combinations were studied,and a large number of results were obtained.A series of hydrogen-based superconductors have been discovered,among which H3S,La H₁₀and other high-temperature superconductors whose superconducting transition temperature is close to room temperature are the most remarkable.Subsequently,the successful synthesis and verification of the experiment triggered a new wave of research on superconducting hydrides.With the deepening of the research,people have tried almost all possible binary combinations,but still have not found a satisfactory answer.With the improvement of computing power and research methods,people turn their attention to ternary hydrides.The addition of the third element greatly expands the spatial configuration and provides more possibilities.So far,the highest superconducting transition temperature is found in the ternary hydride Li₂Mg H₁₆,which can reach the superconducting transition temperature of 473 K at 250 GPa.The C-S-H ternary system successfully synthesized in the 2020 experiment also reached the predicted_of 287 K.These results strongly confirm the research value of ternary hydride system.With further research,new challenges have emerged.Although many high-temperature superconductors near room temperature have been discovered,the high-pressure environment required for synthetic materials has prevented any possible practical applications.So recently,some scientists have begun to search for superconductors that can survive under environmental pressures.In the search for low-voltage superconductivity,ternary hydrides have also yielded many results,and La BH8 is predicted to have a critical_of about 126 K at 50 GPa.KB₂H₈can reach a_of134-146 K at a low pressure of 12 GPa.In this paper,we attempt to use a method that enhances the chemical precompression effect in binary hydrides by combining different new elements to make the stable pressure of HTS more similar to the ambient pressure.After some searching,it was determined that Ce element,which has similar electronegativity to La element on the periodic table,but has lower mass,was the main research object.By changing the X element of Ce-X-H system,a better structure is sought.We tried a variety of possible element compositions such as B,Be,Ca,La,Fe,Si and so on,analyzed and compared the obtained results,and found some new superconductors.The main achievements are as follows:Two novel Ce Be H₈and Ce BH₈superconductors with Fm3 m、R3 m and C2/m symmetries have been discovered by means of crystal structure prediction and first-principles calculations.Through the selection and adjustment of X element,the stable pressure of Fm3 m-Ce Be H₈is reduced to 10Gpa,which the_is about 57 K.This is an unprecedented low pressure in ternary hydrides superconductivity,which also confirms the feasibility of the method.R3 m-Ce Be H₈and C2/m-Ce Be H₈are stable above 20 Gpa and 50 Gpa respectively,with the maximum_of 30 K and12 K.Fm3 m-Ce BH₈is stable above 120 GPa and reaches a maximum_of 118 K at 150 GPa.R3 m-Ce BH₈and C2/m-Ce BH₈stably exist above 120 GPa and 100 GPa,and reach the maximum_of 123 K and 115 K at 195 GPa and 350 GPa,respectively.Two new superconductors,P6 m2-Ce La H₁₈and R3 m-Ce Ca H₁₆,have been discovered through the crystal structure prediction and first-principles calculation of Ce-La-H and Ce-Ca-H systems.P6 m2-Ce La H₁₈has a stable structure above 170 GPa and reaches a maximum_of 139.7 K at 190GPa.R3 m-Ce Ca H₁₆stabilize above 220 GPa and reaches its maximum_of 110.3K at 250 GPa.These findings preliminarily confirm the feasibility of our method,and the study in this paper is conducive to further exploring the influence of adding elements on the superconductivity of ternary hydrides.It is hoped that the work of this paper can provide some reference value for other research on superconductivity of ternary hydrogen compound in the future.