The Role of Spontaneous Polarization in the Negative Thermal Expansion of Tetragonal PbTiO₃-Based Compounds

Abstract

PbTiO(3)-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO(3)-0.3BiFeO(3) and 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3), whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δz(Pb/Bi)) is weakened in 0.7PbTiO(3)-0.3BiFeO(3) but well-maintained in 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3). There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi-O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides.

Negative Thermal Expansion in the Materials With Giant Magnetocaloric Effect

“…Generally, ZTE can be reached by combining the materials with PTE and NTE coefficients. To meet various demands, lots of efforts have been made to search for NTE materials, and a number of materials have been discovered showing giant NTE, e.g., ZrW 2 O 8 (Mary et al, 1996), CuO nanoparticles (Zheng et al, 2008), (Bi,La)NiO 3 (Azuma et al, 2011), PbTiO 3 -based compounds (Chen et al, 2011), antiperovskite manganese nitrides (Takenaka and Takagi, 2005; Iikubo et al, 2008; Sun et al, 2010a; Song et al, 2011; Wang et al, 2012; Lin et al, 2015), La(Fe,Co,Si) 13 (Huang et al, 2013), MnCoGe-based materials (Zhao et al, 2015), and reduced Ca 2 RuO 4 (Takenaka et al, 2017). Among these NTE materials, the phase-transition-type materials (Takenaka and Takagi, 2005; Iikubo et al, 2008; Sun et al, 2010a; Song et al, 2011; Huang et al, 2013; Zhao et al, 2015) have attracted specific attention.…”

Local Structural Distortion Induced Uniaxial Negative Thermal Expansion in Nanosized Semimetal Bismuth

“…In order to maintain the thermal stability and physical properties, a universal and effective method to tailor the thermal expansion of metal or semimetal is strongly expected. So far, doping method to change the chemical composition is regarded as the most common way 2, 3, 4. The most famous example is invar alloy,5, 6 showing a low coefficient of thermal expansion (CTE) during magnetic transition.…”

Effectively control negative thermal expansion of single-phase ferroelectrics of PbTiO3-(Bi,La)FeO3 over a giant range

“…Among the family of NTE materials, there is one branch of ferroelectrics which behave a general phenomenon that unit cell volume contracts during ferroelectric-to-paraelectric phase transition, such as perovskites of PbTiO 3 (PT)212223, BaTiO 3 24, BiFeO 3 25, and (Bi,La)NiO 3 9, tungsten bronze PbNb 2 O 6 26, and semiconductor GeTe27. It is important to note that all ferroelectrics except PT (RT ~ 490°C)23 exhibit NTE property within a narrow temperature range, e.g.…”