when I studied raman spectroscopy(using 532nm laser) of a NdNiO3 thin film( LaAlO3 ,NdGaO3,SrTiO3 substrate) then fine peak is appeared in every cases but when I used Bulk powder polycrystalline NdNiO3 sample then no peak is appeared,only flat spectra is cominng.Can anyone tell me what is the reason behind that ???