As part of their upcoming Symposium of Byzantine Studies, the Cambridge University Press has released a free collection of articles from their journals about Byzantium.

(actually the Symposium is right now 30 March - 1 April)

Available here (journals) -> https://www.cambridge.org/core/brows...yz_news_290319

You can also check out the whole study section of Cambridge UP -> https://www.cambridge.org/core/journ...-greek-studies