Half-Heusler semiconductors as piezoelectrics

One of the central challenges in materials science is the design of functional and multifunctional materials, in which large responses are produced by applied fields and stresses. A rapidly developing paradigm for the rational design of such materials is based on the first-principles study of a large materials family, the perovskite oxides being the prototypical case. Specifically, first-principles calculations of structure and properties are used to explore the microscopic origins of the functional properties of interest and to search a large space of equilibrium and metastable phases to identify promising candidate systems. In this paper, we use a first-principles rational-design approach to demonstrate semiconducting half-Heusler compounds as a previously-unrecognized class of piezoelectric materials, and to provide guidance for the experimental realization and further investigation of high-performance materials suitable for practical applications.Comment: 5 pages, 3 figues, 3 table

The Effect of Symmetry Lowering on the Dielectric Response of BaZrO3BaZrO_3

We use first-principles density functional theory calculations to investigate the dielectric response of BaZrO$_3$ perovskite. A previous study [Arkbarzadeh {\em et al.} Phys. Rev. B {\bf 72}, 205104 (2005)] reported a disagreement between experimental and theoretical low temperature dielectric constant $\epsilon$ for the high symmetry BaZrO$_3$ structure. We show that a fully relaxed 40-atom BaZrO$_3$ structure exhibits O$_6$ octahedral tilting, and $\epsilon$ that agrees with experiment. The change in $\epsilon$ from high-symmetry to low-symmetry structure is due to increased phonon frequencies as well as decreased mode effective charges.Comment: 4 pages, 2 figure

Hexagonal ABCABC as semiconducting ferroelectrics

We use a first-principles rational-design approach to identify a previously-unrecognized class of ferroelectric materials in the $P63mc$ LiGaGe structure type. We calculate structural parameters, polarization and ferroelectric well depths both for reported and as-yet hypothetical representatives of this class. Our results provide guidance for the experimental realization and further investigation of high-performance materials suitable for practical applications.Comment: 5 pages, 2 figures, 3 table

Antiferroelectric Topological Insulators in Orthorhombic AMgBi Compounds (A=Li, Na, K).

We introduce antiferroelectric topological insulators as a new class of functional materials in which an electric field can be used to control topological order and induce topological phase transitions. Using first principles methods, we predict that several alkali-MgBi orthorhombic members of an ABC family of compounds are antiferroelectric topological insulators. We also show that epitaxial strain and hydrostatic pressure can be used to tune the topological order and the band gap of these ABC compounds. Antiferroelectric topological insulators could enable precise control of topology using electric fields, enhancing the applicability of topological materials in electronics and spintronics

Pb-free Semiconductor Ferroelectrics: A Theoretical Study of Pd-substituted Ba(Ti\u3csub\u3e1-\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3eCe\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e Solid Solutions

We use first-principles density-functional-theory calculations to investigate the ground state structures of Ba(Ti1−xCex)O3 solid solutions containing Pd. Previous studies have shown that the properties of BaTiO3, a Pb-free ferroelectric ABO3 perovskite, can be tailored via B-site substitution. In the present study, we substitute Ce for Ti to increase the overall volume of the perovskite, to then accommodate an O-vacancy-stabilized Pd substitution. Using the LDA+U method, we predict that these proposed materials will display a decreased band gap compared to BaTiO3 while maintaining polarization. These features, combined with their environmentally friendly characteristics make these materials promising candidates for use as semiconducting ferroelectrics in solar-energy conversion devices

Pb-free Ferroelectrics Investigated with Density Functional Theory: SnAl\u3csub\u3e½\u3c/sub\u3eNb\u3csub\u3e½\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e Perovskites

Interest in Pb-free ferroelectrics has intensified as the search for less toxic Pb replacements continues. Since Sn is isoelectronic with Pb, it has generated great interest. Most of this effort has focused on SnTiO3. Even though it shows impressive ferroelectricity in calculations, synthesis has proved elusive.We therefore use density-functional theory (DFT) to investigate B-site alternatives that involve smaller size to promote perovskite phase stability. In this paper, Sn(Al½Nb½)O3 (SAN) is investigated. We demonstrate that SAN is likely to be synthesizable, will be ferroelectric, and perhaps a good piezoelectric material as well. We discuss how cation displacements and their interactions affect the polarization of the solid solution.We also explore the electronic properties of the SAN solid solution and correlate them to the structural findings