My wife has been baking sourdough bread in an enameled cast iron Dutch oven and has been getting a very nice crust. She preheats the pan and oven to 500 °F (260 °C), then puts the dough in the pan, cooks a while at 480 °F (250 °C) covered, then at 450 °F (230 °C) uncovered.  Dutch ovens are round and our main use case is sandwiches, so it would be nice to cook in a rectangular pan.  When I search for them, it appears they are all ceramic.  Does the lower heat conductivity of ceramic make it not form as nice a crust? 
Doesn't matter; you cannot use a ceramic pan with that baking technique. If you heat the ceramic pan to 500F and then add the wet dough, it is likely to crack, and possibly even explode.  Same goes for glass. Ceramic pan maker Emile Henry says:  Never preheat your ceramic baking dish dry, always add cooking oil or some type of liquid to the dish.  You should, instead, find a covered cast-iron loaf pan, such as the one by Staub, or a different baking technique, such as the traditional cold-oven cloche technique. 