  Radio halos are synchrotron radio sources detected in some massive galaxy
clusters. Their Mpc-size indicates that (re)acceleration processes are taking
place in the host cluster. X-ray catalogues of galaxy clusters have been used
in the past to search for radio halos and to understand their connection with
cluster-cluster mergers and with the thermal component of the intra-cluster
medium. More recently, the Sunyaev-Zel'dovich effect has been proven to be a
better route to search for massive clusters in a wider redshift range. With the
aim of discovering new radio halos and understanding their connection with
cluster-cluster mergers, we have selected from the Planck Early source catalog
the most massive clusters, and we have observed with the Giant Metrewave Radio
Telescope at 323 MHz those objects for which deep observations were not
available. We have discovered new peculiar radio emission in three of the
observed clusters finding: (i) a radio halo in the cluster RXCJ0949.8+1708;
(ii) extended emission in Abell 1443 that we classify as a radio halo plus a
radio relic, with a bright filament embedded in the radio halo; (iii) low-power
radio emission is found in CIZA J1938.3+5409 which is ten times below the radio
- X-ray correlation, and represents the first direct detection of the radio
emission in the "upper-limit" region of the radio - X-ray diagram. We discuss
the properties of these new radio halos in the framework of theoretical models
for the radio emission.
