A method of growing a single crystal material using a device that includes a conical plug. The conical plug includes a first portion defining a first conical hole about an axis, the first conical hole having a first angle, and includes a second portion contiguous with the first portion and defining a second conical hole about the axis, the second conical hole having a second angle having the same sign as the first angle and being greater than the first angle. The device includes an upper tube comprising the conical plug fused therein and a seeding well plug. The device includes a lower tube including the seeding well plug fused therein. A single crystal KPb2Cl5 material is grown from the oriented single crystal KPb2Cl5 seed through the first conical hole and then the second conical hole and then with continuing growth in the upper tube.