A device has a M8XY6 layer in between a first conductive layer on the top and a second conductive layer on the bottom, wherein (i) M includes at least one element selected from the following: Cu, Ag, Li, and Zn, (ii) X includes at least one Group XIV element, and (iii) Y includes at least one Group XVI element. Another device has MaXbYc material contacted on opposite sides by respective layers of conductive material, wherein: (i) M includes at least one element selected from the following: Cu, Ag, Li, and Zn, (ii) X includes at least one Group XIV element, and (iii) Y includes at least one Group XVI element, and a is in the range of 48-60 atomic percent, b is in the range of 4-10 atomic percent, c is in the range of 30-45 atomic percent, and a+b+c is at least 90 atomic percent.