Can sonata form be used in a slow movement?

Yes, sonata form can be used in a slow movement. While it is most strongly associated with the first movements of Western instrumental genres, it is not restricted to fast tempos or initial movements.123

When composers employ sonata form for a slow movement, they often adapt the structure to suit the tempo. Specifically, the demands of maintaining overall musical proportion frequently lead to the omission of the development section.1

Although other patterns—such as simple ternary form or theme and variations—are common for slow movements, sonata form remains a recognized option for providing the necessary range of thematic development and contrast within a multimovement work.12