The MMSZ4705 from Micro Commercial Components is a Zener Diode with Zener Voltage 18 to 18.9 V, Zener Current 50 mA(zener test current), Voltage Forward 0.95 V, Current Reverse Leakage Current:- 0.05 uA, Power 500 mW. More details for MMSZ4705 can be seen below.