Disclosed are ceramic powder compositions that include Si, N, O, C, Mg, and/or Mn in tailored combinations of different crystalline phases for producing high temperature resistant and high strength ceramic products. In some aspects, a ceramic powder for producing high temperature-resistant and/or high mechanical strength materials comprises a silicon nitride (Si3N4) powder, comprising Si3N4 particles having a size within a range of 30 nm to 700 nm, wherein the Si3N4 powder include alpha and beta phase silicon nitride in an amount up to about 1-100% vol; and an impurity constituent intermixed with the Si3N4 powder within the ceramic powder, the impurity constituent comprising at least one of silicon (Si), nitrogen (N), oxygen (O), carbon (C), magnesium (Mg), or manganese (Mn), wherein the impurity constituent constitutes less than about 0.1% wt to 15% wt of the ceramic powder.