you are way too cryptic! Unless you specify what kind of reaction you do, it's kind of hard to guess! Remember carbonates decompose into oxides if you do not pay attention
Please specify your compound. A single compound can have many different phase, which will be reflected in XRD. For example when your are preparing (Ba,Ca)TiO3, you will endup with 2-3 different phases even after heating till 1300C. There are methods to avoid it.