can we use only ipv6 address

Correct: As soon as you disable IPv4 you lose all communication to IPv4-only systems. The IPv6 over IPv4 tuels are meant for people of which the ISP does not provide an exteal IPv6 address.

What you are looking for is a 6to4 proxy, but so far I've not found any that do this, especially if your ISP does not support IPv6 yet.

Edit: You could look into 4in6 methods, to allow your IPv4 traffic to be tueled.