The growth and properties of electronic oxide thin films are reviewed. In particular, the synthesis and properties of superconducting, insulating, conducting, magnetic, and semiconducting epitaxial oxide structures are discussed. Crystal structures and functional properties common to many oxide materials are briefly reviewed. A description of film-growth techniques follows. Finally, an extensive overview of the epitaxial growth for specific oxide material systems is given. This includes the epitaxial growth of electronic oxide thin films on oxide and non-oxide substrates.

Synthesis and properties of epitaxial electronic oxide thin-film materials

Transparent oxides are essential building blocks to many technologies, ranging from components in transparent electronics, transparent conductors, to absorbers and protection layers in photovoltaics and photoelectrochemical devices. However, thus far, it has been difficult to develop p-type oxides with wide band gap and high hole mobility; current state-of-art transparent p-type oxides have hole mobility in the range of < 10 cm$^2$/Vs, much lower than their n-type counterparts. Using high-throughput computational screening to guide the discovery of novel oxides with wide band gap and high hole mobility, we report the computational identification and the experimental verification of a bismuth-based double-perovskite oxide that meets these requirements. Our identified candidate, Ba$_2$BiTaO$_6$, has an optical band gap larger than 4 eV and a Hall hole mobility above 30 cm$^2$/Vs. We rationalize this finding with molecular orbital intuitions; Bi$^{3+}$ with filled s-orbitals strongly overlap with the oxygen p, increasing the extent of the metal-oxygen covalency and effectively reducing the valence effective mass, while Ta$^{5+}$ forms a conduction band with low electronegativity, leading to a high band gap beyond the visible range. Our concerted theory-experiment effort points to the growing utility of a data-driven materials discovery and the combination of both informatics and chemical intuitions as a way to discover future technological materials.

/pdf/high-mobility-bismuth-based-transparent-p-type-oxide-from-46aigkkrve.pdf

High-Mobility Bismuth-based Transparent p-Type Oxide from High-Throughput Material Screening

Non-symmorphic materials have recently been predicted to exhibit many different exotic features in their electronic structures. These originate from forced band degeneracies caused by the non-symmorphic symmetry, which not only creates the possibility to realize Dirac semimetals, but also recently resulted in the prediction of novel quasiparticles beyond the usual Dirac, Weyl or Majorana fermions, which can only exist in the solid state. Experimental realization of non-symmorphic materials that have the Fermi level located at the degenerate point is difficult, however, due to the requirement of an odd band filling. In order to investigate the effect of forced band degeneracies on the transport behavior, a material that has such a degeneracy at or close to the Fermi level is desired. Here, we show with angular resolved photoemission experiments supported by density functional calculations, that ZrSiTe hosts several fourfold degenerate Dirac crossings at the X point, resulting from non-symmorphic symmetry. These crossings form a Dirac line node along XR, which is located almost directly at the Fermi level and shows almost no dispersion in energy. ZrSiTe is thus the first real material that allows for transport measurements investigating Dirac fermions that originate from non-symmorphic symmetry.

https://iopscience.iop.org/article/10.1088/1367-2630/aa4f65/pdf

Non-symmorphic band degeneracy at the Fermi level in ZrSiTe

Perovskite-type structures (ABO3) have received significant attention because of their crystallographic aspects and physical properties, but there has been no clear evidence of a superconductor with a double-perovskite-type structure, whose different elements occupy A and/or B sites in ordered ways. In this report, hydrothermal synthesis at 220 °C produced a new superconductor with an A-site-ordered double perovskite structure, (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12, with a maximum Tc  of about 27 K.

Superconducting Double Perovskite Bismuth Oxide Prepared by a Low‐Temperature Hydrothermal Reaction

The phase diagram of BaPb(1-x)Bi(x)O3 exhibits a superconducting dome in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high-resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare with the Ginzburg-Landau coherence length. We find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.

/pdf/stripe-like-nanoscale-structural-phase-separation-in-16fhrnk1ra.pdf

Stripe-like nanoscale structural phase separation in superconducting BaPb1-xBixO3

Ba1−x
K x
 BiO3(BKBO) has aT

 c
 (onset) of 34 K. It is the highest-temperature oxide superconductor which is cubic, with a coherence length of 30–60 A. The basic properties of this compound are reviewed.

B. A. Baumert

Papers

Barium potassium bismuth oxide: A review