  Perovskite oxides containing transition metals are promising materials in a
wide range of electronic and electrochemical applications. However, neither
their work function values nor an understanding of their work function physics
have been established. Here, we predict the work function trends of a series of
perovskite ($ABO_3$ formula) materials using Density Functional Theory, and
show that the work functions of (001)-terminated AO- and $BO_2$-oriented
surfaces can be described using concepts of electronic band filling, bond
hybridization, and surface dipoles. The calculated range of AO ($BO_2$) work
functions are 1.60-3.57 eV (2.99-6.87 eV). We find an approximately linear
correlation ($R^2$ between 0.77-0.86, depending on surface termination) between
work function and position of the oxygen 2p band center, which correlation
enables both understanding and rapid prediction of work function trends.
Furthermore, we identify $SrVO_3$ as a stable, low work function, highly
conductive material. Undoped (Ba-doped) $SrVO_3$ has an intrinsically low
AO-terminated work function of 1.86 eV (1.07 eV). These properties make
$SrVO_3$ a promising candidate material for a new electron emission cathode for
application in high power microwave devices, and as a potential electron
emissive material for thermionic energy conversion technologies.
