Multicomponent Structural Design,Synthesis And Properties Of Novel Copper-Antimony (Bismuth)-Based Chalcogenides

The development and utilization of new energy materials is one of the important ways to solve the energy crisis and environmental pollution.The chalcogenide is one of the most important branches in the field of inorganic chemistry due to their structural diversities and various physical properties.Especially in the field of the photoelectric conversion and thermoelectric materials,copper antimony?bismuth?based chalcogenides show their potential applications.Copper antimony?bismuth?based chalcogenides have been proposed as earth abundant and low toxic materials,which also have complex structures and unique physical properties.However,due to bad thermal stability,poor electron mobility and low Seebeck coefficient?S?for intrinsic compounds,their efficiencies of thermoelectricity and photoelectricity are still low.Therefore,it is beneficial to design and synthesize new cost effective copper antimony?bismuth?based chalcogenides to satisfy the requirement of high performing thermoelectric or photoelectric materials.Therefore,in this thesis,we started with loosely packed and conductive structures Cu Sb?Bi?Q?Q=S,Se,Te?as the main motifs,used the concept of multicomponent materials and introduced electron/phonon insulating building blocks to synthesize the desired copper antimony?bismuth?based chalcogenides.With the help of these concepts and design,new compounds with enhanced thermal stability,low thermal conductivity?k?,high S and enhanced abilities of electron hole separation and transport were obtained.We also investigated the physical properties,phonon and electronic structures of these chalcogenides,and explored their relationship between thermoelectric?TE?or photoelectric properties and crystal structures.The main research contents and innovative achievements are stated as follows:1)Insulating Channels/Conductive Frameworks of Novel Cu-Sb-Se?Te? Compounds:Due to the concept of multicomponent materials,we chose the Cu Sb Se?CASe?system and design new compounds by intercalating an ionic unit SrO into the channels of Cu₃SbSe₃.Finally,we synthesized a large three dimensional?3D?framework structure Sr₃O₃Cu₃SbQ₃?Q=Se,Te?by solid state methods.Sr₃O₃Cu₃SbTe₃crystallizes in the trigonal system of space group C _{3 v}⁵ R3m?No.160?,which represents a new structure type.It features anisotropic 3D framework[Cu₃SbO₃Te₆]¹²,in which the adjacent[Cu₃SbO₃Te₆]¹22 clusters connect with each other by vertices sharing and leave a big cage occupied by the Sr²⁺ions.The band gap of this compound is 2.02 eV.The Sr₃O₃Cu₃SbTe₃ shows a reversible phase transition around 600 K and a very low k?k=0.38 W·m ¹·K ¹?,which can be own to highly vibration of the liquid like Cu atoms at high temperature.Furthermore,Sr₃O₃Cu₃SbTe₃ also shows a high conductivity??=54.09 S·cm ¹?.As a result,a maximum ZT is 0.11 at 800 K.Such a low lattice thermal conductivity?k _L?is mainly attributed to the effect of the“restlessness”of Cu atoms and the rattling Te/Sr atoms.2)Insulating Layers/Conductive Layers of Novel Cu-Sb-S?Se?Compounds:We chose the layered Cu Sb S?Se?compounds and design new compounds by intercalating an ionic unit SrO into the van der Waals?VDW?gap of CuSbSe₂ and CuSbS₂.Finally,we have successfully synthesized a new quasi 2D compound SrOCuSbQ₂?Q=Se,S?by traditional melting salt method and hydrazine hydrothermal method,respectively.The SrOCuSbSe₂ compound crystallizes in the C _{2 h}² P2₁/m?No.11?space group of the monoclinic system,it has a quasi 2D layered structure.The structure features_?²[CuSbSe₂O]² anionic layers,which are separated by Sr²⁺ions.The crystal structure presents separation between electronic insulation units?EIU?SrO layers and electronic conduction units?ECU?CuSbSe₂ layers.The compound reveals an indirect band gap of 1.56 eV,in accord with semiconductive properties.The as synthesized SrOCuSbSe₂ compound possesses an anisotropic TE properties with very low k?k=0.38 W·m ¹·K ¹?and extremely high S?S=718.18?V·K ¹?.The extremely high S with anisotropy may be related to this multicomponent structure wherein insulating SrO layers and conductive CuSbSe₂ layers alternate forming a natural superlattice with two dimensional confinement of charge carriers.The low k_L is mainly attributed to the effect of lone pair electrons of Sb atoms and SrO EIU layers intercalation.As a result,its maximum ZT is 0.22 at 850 K.SrOCuSbS₂ shows optical band gap of 1.90 eV.Due to intercalation of EIU SrO,the structure creates strong 2D confinement of charge carriers and reduces recombination of photogenerated carriers from other directions.Finally,it has a high photoelectric density of 1.88 mA/cm² at 1V and a reversible photocurrent response.3)Insulating Layers/Conductive Layers of Novel Cu-Bi-Se Compounds:In accordance with the concept of multicomponent materials,we design a new compound by intercalating an ionic unit SrO into the layer of CuBiSe₂ and finally synthesized a new quasi 2D compound SrOCuBiSe₂ by solid state methods.The SrOCuBiSe₂ is isostructural with SrOCuSbSe₂.The crystal structure can be regarded as combination of EIU SrO units and ECU CuBiSe₂ layers.The band gap of this compound is 1.33 eV.SrOCuBiSe₂ shows a high conductivity??=890.12 S·m ¹?,high S?S=455.02?V·K ¹?and low k?k=0.45 W·m ¹·K ¹?.The merit of ZT value is 0.06 at 800 K.According to the DFT phonon calculations,the lone pair electrons of the Bi atoms and the Cu rattlers strengthen crystal anharmonicity and result in low k_L.In addition,the SrOCuBiSe₂ have stronger anharmonicity and lower k_L compared with SrOCuSbSe₂.