beta-Si3N4　seed　crystals　were　synthesized　by　sintering　(alpha+beta)-Si3N4　powders　with　Y2O3+MgO　additives　at　1800　degrees　C.　Full　alpha-　to　beta-phase　transformation　was　achievable　at　1800　degrees　C　for　1　h.　The　pre-existing　beta-Si3N4　particles　acted　as　nuclei　during　a　sintering　process.　The　length　and　mean　aspect　ratio　of　beta-Si3N4　seed　grains　could　be　tailored　by　careful　control　of　alpha/beta-Si3N4　ratio,　which　resulted　in　various　nuclei　and　driving　force.　The　sample　A95B5　with　5%　beta-nuclei　shows　a　bimodal　size　distribution　containing　large　amount　of　abnormal　elongated　beta-Si3N4　grains　with　remarkable　large　diameter.　With　increasing　the　beta-phase　content　from　5　wt%　to　100　wt%,　the　average　diameter　and　aspect　ratio　of　the　beta-Si3N4　single　crystals　decreased　from　1.43　mu　m　to　0.92　mu　m　and　from　4.36　to　2.79,　respectively.　(C)　2014　Elsevier　Ltd　and　Techna　Group　S.r.l.　All　rights　reserved.