The MMSZ4678 from Micro Commercial Components is a Zener Diode with Zener Voltage 1.8 to 1.89 V, Zener Current 50 mA(zener test current), Voltage Forward 0.95 V, Current Reverse Leakage Current:- 7.5 uA, Power 500 mW. More details for MMSZ4678 can be seen below.