  The maximum luminosity of type Ia supernovae (SNe Ia) depends on the oxygen
abundance of the regions of the host galaxies where they explode. This
metallicity dependence reduces the dispersion in the Hubble diagram (HD) when
included with the traditional two-parameter calibration of SN Ia light-curve
(LC) parameters and absolute magnitude. In this work, we use empirical
calibrations to carefully estimate the oxygen abundance of galaxies hosting SNe
Ia from the SDSS-II/SNe Survey at intermediate redshift, by measuring their
emission line intensities. We also derive electronic temperature with the
direct method for a small fraction of objects for consistency. We find a trend
of decreasing oxygen abundance with increasing redshift for the most massive
galaxies. Moreover, we study the dependence of the HD residuals (HR) with
galaxy oxygen abundance obtaining a correlation in line with those found in
other works. In particular, the HR vs oxygen abundance shows a slope of
-0.186$\pm$0.123 mag dex$^{-1}$ (1.52$\sigma$), in good agreement with
theoretical expectations. This implies smaller distance modulii after
corrections for SNe Ia in metal-rich galaxies. Based on our previous results on
local SNe Ia, we propose this dependence to be due to the lower luminosity of
the SNe Ia produced in more metal-rich environments.
