I need one best Phase change material which must be semi solid when adding heat, for my research i need less than or equal to 40 degree Celsius melting point.
As Dr. Yehia suggested, paraffin undoubtedly fulfills all the merits that you expect. Nevertheless, low thermal conductivity is a major challenge in the real game, say heating ventilation and air conditioning.
This paper presents analysis of plenty of phase change materials commercially available. See if this helps:
The one phase change material most readily available and low cost in India are organic ones while paraffin would not stand effective as it’s not available in India and needs to be imported. You can contact www.pluss.co.in for inquiries and samples.
If a melting temperature of 29 degree Celsius is not too low for your application, calcium chloride hexahydrate could be interesting for you: melting enthalpy approx. 190 J/g, costs below 0.50 €/kg using technical grade calcium chloride.
I would suggest paraffin PCM as opposed to salt hydrates, which have very high degree of supercooling. Since you are focusing at mushy phase of PCM, paraffin would provide an ideal solution. You can choose the paraffin at your desired melting temperature.