压力对PbTiO_(3)结构和热物性质影响的第一性原理研究  

Pressure on the Structure and Thermal Properties of PbTiO_(3):First-principle Study

作　　者：文志勤 黄彬荣 卢涛仪 邹正光[1] WEN Zhiqin;HUANG Binrong;LU Taoyi;ZOU Zhengguang(School of Materials Science and Engineering,Guilin University of Technology,Guilin 541004,China)

机构地区：[1]桂林理工大学材料科学与工程学院,桂林541004

出　　处：《无机材料学报》2022年第7期787-794,共8页Journal of Inorganic Materials

基　　金：广西自然科学基金(2019GXNSFBA245092,2019GXNSFGA245006);桂林理工大学科研启动金(GUTQDJJ2019116)。

摘　　要：PbTiO_(3)是一种重要的铁电功能材料,但压力对其结构、稳定性、力学和热力学性能的影响尚不明确,从而限制了其在电子通讯领域的应用。本研究采用基于密度泛函理论的第一性原理方法,研究了压力下四方铁电相钛酸铅(TP-PTO)、立方顺电相钛酸铅(CP-PTO)、四方前驱体相钛酸铅(PP-PTO)结构和热物性质。研究发现,三种结构可压缩性由大到小依次为PP-PTO>TP-PTO>CP-PTO。能带结构和态密度均表明PTO在研究的压力范围内未发生相变。PTO带隙随着压力增大逐渐降低,TP-PTO在20 GPa由间接带隙半导体转变为直接带隙半导体,其余两相在压力下恒为直接带隙半导体。PTO在0~30 Gpa范围力学稳定,且具有各向异性,其综合力学性能随着压力的增加而增强,各向异性则是先降低后升高。通过准谐德拜近似理论研究了温度和压力对PTO德拜温度、熵、热容的影响,结果表明德拜温度随着温度上升而下降,随着压力增大而上升,反映出共价键强度依次为CP-PTO>TP-PTO>PP-PTO。熵和热容随着温度上升而上升,随着压力的增大而下降。PbTiO_(3)(PTO)is an important ferroelectric functional material,but its structure,stability,mechanical property,and thermodynamic property under pressure is still unknown,leading to restriction in applying in the field of electronic communication.Here,first-principles calculations based on density functional theory was performed to study the structure and thermal properties of pre-perovskite phase PbTiO_(3)(PP-PTO),ferroelectric tetragonal phase PbTiO_(3)(TP-PTO),and paraelectric cubic phase PbTiO_(3)(CP-PTO)under pressure.It is found that their compressibility in descending order is PP-PTO>TP-PTO>CP-PTO.Under considered pressure,three PTO phases have not undergone a phase transition analyzed by band structure and density of states,and their band gap gradually decreases with increasing pressure.Among them,the TP-PTO changes from an indirect to a direct band gap semiconductor at 20 GPa,while the others remain a direct band gap semiconductor.Those PTO phases are mechanically stable and anisotropy from 0 to 30 GPa.Furthermore,their comprehensive mechanical properties increase and anisotropy firstly decreases and then increases with increasing pressure.Analysis based on quasi-harmonic Debye approximation theory was performed to study the influence of temperature and pressure on Debye temperature,entropy and heat capacity.The results illuminate that Debye temperature decreases with temperature increase,nevertheless,pressure has the opposite effect,which elucidates that the order of covalent bond from strong to weak is CP-PTO>TP-PTO>PP-PTO.Entropy and heat capacity of PTO increase with rising temperature,but decrease with the increase of pressure.

关 键 词：钛酸铅 电子结构 弹性力学 第一性原理 

分 类 号：TQ174[化学工程—陶瓷工业]