How can I Change the scale/ticks on a semilog plot (R2017b)?

Hi,

I'm trying to plot a graph with a logarithmic scale on the x axis starting from 200 then increasing in decades. At the moment I am only able plot it with the graph going in decades of 10^x. I'd like to change this so that it goes in decades of 2*10^x and the grid changes appropriately.

This is what I have currently:

Thanks.