Graduation Year

2024

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Physics

Major Professor

Inna Ponomareva, Ph.D.

Co-Major Professor

Sergey Lisenkov, Ph.D.

Committee Member

Hariharan Srikanth, Ph.D.

Committee Member

Lilia Woods, Ph.D.

Committee Member

Jacob Gayles, Ph.D.

Keywords

Formates, Perovskites, Ferroelectricity, Piezoelectricity, Dielectricity

Abstract

Formate perovskites, denoted as AB(HCOO)3, represent a diverse group of hybrid organic-inorganic compounds, renowned for their numerous phase transitions and a wide array of properties. These properties encompass (anti)ferroelectricity, ferroelasticity, (anti)ferromagnetism, and multiferroism. Despite extensive research on these materials, a comprehensive examination of their properties across a substantial number of formate perovskites remains scarce. This scarcity stems from structural complexity of these materials, potential systematic errors arising from different measurement techniques or incomplete data. For instance, data for critical parameters like piezoelectricity, dielectricity, and elasticity tensors have been lacking.

In this study, we address these challenges by employing first-principles density functional theory simulations. Our work provides a comprehensive assessment of structural, mechanical, dielectric, piezoelectric, and ferroelectric properties for 29 distinct formate perovskites. Our findings reveal a broad spectrum of characteristics within this family, including elastic stiffness ranging from 0.5 to 127.0 GPa, highly anisotropic linear compressibility, encompassing zero and even negative values, dielectric constants spanning from 0.1 to 102.1, and a highly anisotropic piezoelectric response with longitudinal values ranging from 1.18 to 21.12 pC/N. Additionally, we identify spontaneous polarizations within the range of 0.2 to 7.8 µC/cm2. Furthermore, our study introduces and computationally characterizes previously unreported formate perovskite compounds.

The quest for flexible, lead-free, low temperature synthesizable alternatives to the tradition ferroelectric oxides has instigated the search for ferroelectrics in metal-organic frameworks (MOFs). One of the sub-classes of MOFs, the hybrid formate perovskites (HFPs), habors materials which have been proven experimentally and computationally to be ferroelectric. However, the values of polarization recorded so far for HFPs are rather low, like ten orders of magnitude lower than those of traditional perovskite oxides. Therefore, it is essential to dissect the polarization contributions from the structural entities of HFPs, majorly the framework and molecules, in an attempt to identify the major driver of ferroelectricity. Thus, in this work, we have identified contributions to the total spontaneous polarization from seven ferroelectric members of hybrid formate perovskites.

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