Guided design of copper oxysulfide superconductors

Abstract

We describe a framework for designing novel materials, combining modern first-principles electronic structure tools, materials databases, and evolutionary algorithms capable of exploring large configurational spaces. Guided by the chemical principles introduced by Antipov, et. al., for the design and synthesis of the Hg-based high-temperature superconductors, we apply our framework to design a new layered copper oxysulfide, Hg(CaS)2CuO2. We evaluate the prospects of superconductivity in this oxysulfide using theories based on charge-transfer energies, orbital distillation and uniaxial strain.The superconductors with the highest known transition temperatures at ambient pressure are all layered compounds containing planes of copper and oxygen where the superconducting electrons reside, separated by "spacer layers" composed of other elements. For a given compound, varying the doping level to an optimal value near 0.15 holes per copper maximizes the superconducting transition temperature T c . Since the copper oxide planes are a common ingredient, the large variabilty in optimal T c 's between compounds must then be controlled by the spacer layers, which function to tune the chemical and structural properties of the copper oxide layer. Finding novel compositions for the spacer layers is key to discovering new superconductors with higher transition temperatures.Theoretical design of new compounds is challenging due to the vast combinatorial space of elements and the large number of constraints: preferred oxidation state, electronegativity, atomic radii, preferred local coordination environment, and overall electrical neutrality. These microscopic properties in turn determine the local structural stability, global configurational minimum, and thermodynamic stability. Finding the global low-energy structure is the computational bottleneck. If a given composition results in a stable compound, we still need to determine whether it tunes the low-energy Hamiltonian so that T c is enhanced, which imposes further screening criteria.Rather than design a compound from scratch, we adopt a more moderate approach: we take as a starting point the family of cuprates with the highest transition temperatures, the Hg-based cuprates, and modulate its spacer layers. We benefit from the vast body of chemical intuition accumulated for the cuprates, for instance, laid out especially clearly in Ref. 1, and use modern electronic structure methods [2,3], materials databases [4,5] and evolutionary algorithms [6] to efficiently screen for compositions which have the desired structure and the best prospects for stability. We use three proposed theories, based on epitaxial strain [7], the charge-transfer energy [8], and orbital distillation [9], to evaluate the resultant compound's prospects for superconducivity. In this manuscript, we describe the general framework for guided design of new materials, and demonstrate its workflow by applying the principles to design a new layered copper oxysulfide Hg(CaS) 2 CuO 2 , which we abbreviate (HC-SCO). ...

Correlated materials design: prospects and challenges

“…With the experience of the previous section we revisit the question of how to design novel cuprates following Ref. 140. The challenge in the design process is finding a new chemical composition that forms in the desired cuprate structure -with slightly different parameters, thus enabling the elucidation of the mechanism of superconductivity.…”

Similarities and differences between infinite-layer nickelates and cuprates and implications for superconductivity

“…Units are meV. i ranges in the table from 0 to 5, and corresponds to lattice vectors (0,0,0), (1,0,0), (1,1,0), (2,0,0), (0,0,1) and (0,0,2 [23].…”

Oxysulfide LiAlSO: A Lithium Superionic Conductor from First Principles

“…Discovering oxysulfide superionic conductors may combine the extremely high ionic conductivity of sulfides with the excellent stability of oxides.It is not uncommon for oxysulfide compounds to be found in various applications. For example, rare-earth oxysulfides have technological importance because of their exceptional luminescent efficiencies [16], and bulk superconductivity has been identified in bismuth and copper oxysulfides [17]. Transition-metal-based oxysulfides act as photocatalysts in the decomposition of water [18].…”