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We present a broad-band map of polarized diffuse emission at 167–198 MHz developed from data from the Murchison Widefield Array (MWA). The map is designed to improve visibility simulation and precision calibration for 21 cm Epoch of Reionization (EoR) experiments. It covers a large swath – 11 000 sq. deg. – of the Southern hemisphere sky in all four Stokes parameters and captures emission on angular scales of 1–9°. The band-averaged diffuse structure is pre-dominantly unpolarized but has significant linearly polarized structure near RA  = 0 h. We evaluate the accuracy of the map by combining it with the GLEAM catalogue and simulating an observation from the MWA, demonstrating that the accuracy of the short baselines (6.1–50 wavelengths) now approaches the accuracy of the longer baselines typically used for EoR calibration. We discuss how to use the map for visibility simulation for a variety of interferometric arrays. The map has potential to improve calibration accuracy for experiments such as the Hydrogen Epoch of Reionization Array and the forthcoming Square Kilometre Array as well as the MWA.

Using molten‐salt synthetic techniques, NaNbO₃(Space groupPbcm; No. 57) was prepared in high purity at a reaction time of 12 hours and a temperature of 900°C. All NaNbO₃products were prepared from stoichiometric ratios of Nb₂O₅and Na₂CO₃together with the addition of a salt flux introduced at a 10:1 molar ratio of salt to NaNbO₃, that is, using the Na₂SO₄, NaF, NaCl, and NaBr salts. A solid‐state synthesis was performed in the absence of a molten salt to serve as a control. The reaction products were all found to be phase pure through powder X‐ray diffraction, for example, with refined lattice constants ofa = 5.512(5) Å,b = 5.567(3) Å, andc = 15.516(8) Å from the Na₂SO₄salt reaction. The products were characterized using UV‐Vis diffuse reflectance spectroscopy to have a bandgap size of ~3.5 eV. The particles sizes were analyzed by scanning electron microscopy (SEM) and found to be dependent upon the flux type used, from ~<1 μm to >10 μm in length, with overall surface areas that could be varied from 0.66 m²/g (for NaF) to 1.55 m²/g (for NaBr). Cubic‐shaped particle morphologies were observed for the metal halide salts with the set of exposed (100)/(010)/(001) crystal facets, while a truncated octahedral morphology formed in the sodium sulfate salt reaction with predominantly the set of (110)/(101)/(011) crystal facets. The products were found to be photocatalytically active for hydrogen production under UV‐Vis irradiation, with the aid of a 1 wt% Pt surface cocatalyst. The platinized NaNbO₃particles were suspended in an aqueous 20% methanol solution and irradiated by UV‐Vis light (λ > 230 nm). After 6 hours of irradiation, the average total hydrogen production varied with the particle morphologies and sizes, with 753 µmol for Na₂SO₄, 334 µmol for NaF, 290 µmol for NaCl, 81 µmol for NaBr, and 249 µmol for the solid‐state synthesized NaNbO₃. These trends show a clear relationship to particle sizes, with smaller particles showing higher photocatalytic activity in the order of NaF > NaCl > NaBr. Furthermore, the particle morphologies obtained from the Na₂SO₄flux showed even higher photocatalytic activity, though having a relatively similar overall surface area, owing to the higher activity of the (110) crystal facets. The apparent quantum yield (100 mW/cm²,λ = 230 to 350 nm, pH = 7) was measured to be 3.7% for NaNbO₃prepared using the NaF flux, but this was doubled to 6.8% when prepared using the Na₂SO₄flux. Thus, these results demonstrate the powerful utility of flux synthetic techniques to control particle sizes and to expose higher‐activity crystal facets to boost their photocatalytic activities for molecular hydrogen production.