Minecraft from ps3 to ps4?

You can't download PS3 Minecraft to PS4. The PS4 version is out now. You can transfer PS3 Minecraft data to the PS4 but not the actual game.

Transfer data from the PS3 to PS4 or PS Vita

To transfer worlds created on the PS3 to the PS4 or PS Vita, launch Minecraft on the PS3 and click on "Play Game" from the list of options. Select the saved world you would like to transfer, press the R1 button on the controller, select Upload Save for PS Vita/PS4 and press the X button.