Periodical refers to a publication that is issued regularly that contains different information that is meant to be read by a lot of readers. General periodicals and specialized periodicals are two major types of periodicals. General periodicals are issued regularly to give concise information in the form of magazines about common things like sports, time, etc.
Specialized periodicals are mostly read by professionals because they are written as journals for different kinds of fields. Journals, on the other hand, are just a subset or type of periodical, although it has several interpretations. Most newspapers that are being produced every day can be considered as journals.
Academic journals are also a type of journal, plus magazines. At times, a journal can be referred to as a publication that contains records of events or transactions. In short, a periodical is a broad term, whereas a journal is usually considered to be part of a periodical.