We present the stellar mass (M*)–gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts (0.5 ≤ z ≤ 0.7) for for 1381 field galaxies collected from deep spectroscopic surveys. The star formation rate (SFR) and color at a given M* of this magnitude-limited (R ≲ 24 AB) sample are representative of normal star-forming galaxies. For masses below 109 M☉ our sample of 237 galaxies is ~10 times larger than those in previous studies beyond the local universe. This huge gain in sample size enables superior constraints on the MZR and its scatter in the low-mass regime. We find a power-law MZR at 108 at M☉ \u3c M* \u3c 1011 M☉: 12 + log(O/H) = (5.83 ± 0.19) + (0.30 ± 0.02) log(M*/M☉). At 109 M☉ \u3c M* \u3c 1010.5 M☉, our MZR shows agreement with others measured at similar redshifts in the literature. Our power-law slope is, however, shallower than the extrapolation of the MZRs of others to masses below 109 M☉. The SFR dependence of the MZR in our sample is weaker than that found for local galaxies (known as the fundamental metallicity relation). Compared to a variety of theoretical models, the slope of our MZR for low-mass galaxies agrees well with predictions incorporating supernova energy-driven winds. Being robust against currently uncertain metallicity calibrations, the scatter of the MZR serves as a powerful diagnostic of the stochastic history of gas accretion, gas recycling, and star formation of low-mass galaxies. Our major result is that the scatter of our MZR increases as M* decreases. Our result implies that either the scatter of the baryonic accretion rate (σ Ṁ) or the scatter of the M* –Mhalo relation (σ SHMR) increases as M* decreases. Moreover, our measure of scatter at z = 0.7 appears consistent with that found for local galaxies. This lack of redshift evolution constrains models of galaxy evolution to have both σ Ṁ and σ SHMR remain unchanged from z = 0.7 to z = 0
