There is no description for submit buttons in material design. The most closest by meaning are floating action buttons. The buttons are located in top part of screen, but I don't see any sense in this solution for the form. Because user fill the form up -> down, left -> right, and logical place for the button is down right corner.
We made mobile app with material button and usual button in down right corner:
Don't look at other elements or icons, look only at position of orange button.
We compare them on A/B test, there was only button position changing and second version (with down-right corner button) had won. But this version is a little bit ugly and now bottom of screen is overweighted.
What should we do with this button?