Context :

Aims : To gain futher insight on the origin of diffuse radio sources in galaxy clusters and their connection with cluster merger processes , we performed GMRT low frequency observations of the radio halos , relics and new candidates belonging to the GMRT Radio Halo Cluster Sample first observed at 610 MHz .
Our main aim was to investigate their observational properties and integrated spectrum at frequencies below 610 MHz .

Methods : High sensitivity imaging was performed using the GMRT at 325 MHz and 240 MHz .
The properties of the diffuse emission in each cluster were compared to our 610 MHz images and/or literature information available at other frequencies , in order to derive the integrated spectra over a wide frequency range .

Results : Cluster radio halos form a composite class in terms of spectral properties .
Beyond the classical radio halos , whose spectral index \alpha is in the range \sim 1.2 \div 1.3 ( S \propto \nu ^ { - \alpha } ) , we found sources with \alpha \sim 1.6 \div 1.9 .
This result supports the idea that the spectra of the radiating particles in radio halos is not universal , and that inefficient mechanisms of particle acceleration are responsible for their origin .
We also found a variety of brightness distributions , i.e .
centrally peaked as well as clumpy halos .
Even though the thermal and relativistic plasma tend to occupy the same cluster volume , in some cases a positional shift between the radio and X–ray peaks of emission is evident .
Our observations also revealed the existence of diffuse cluster sources which can not be easily classified either as halos or relics .
New candidate relics were found in A 1300 and in A 1682 , and in some clusters “ bridges ” of radio emission have been detected , connecting the relic and radio halo emission .
Finally , combining our new data with literature information , we derived the LogL _ { X } –LogP _ { 325 ~ { } MHz } correlation for radio halos , and investigated the possible trend of the spectral index of radio halos with the temperature of the intracluster medium .

Conclusions :