There are different types of IUDs, some of which are no longer manufactured. I didn’t and am not going to read the articles you posted, but here is what I’ve heard.
The IUDs in general induce a “foreign body” reaction with the body’s immune system. White blood cells engulf the embryo and prevent implantation, i.e. the embryo has no nutritional source to grow unless it attaches to the lining of the uterus, but it can’t. This effect is enhanced by copper interfering with normal enzymatic reacions in the tissue as well as local metabolic effects. Some IUDs also contained progesterone, a hormone which also suppress growth in the lining, suppresses ovulation (in about 40% of women at 65 mcg progesterone/day) and thickening the cervical mucus plug to prevent sperm motility. I seriously doubt copper replaces zinc in the acrosome of the sperm but am saying this off the top of my head. Only Copper-Ts are currently used in Canada TTBOMK.
There’s no reason IUDs can’t work in several ways and they probably do. They are effective within 24 hours of insertion and need to be replaced every 1-3 years (depending on model, the older “inert” ones no longer made last even longer). The failure rate varies between 0.5-5/100 women-years depending on model. Contraindications include pregnancy, undiagnosed dysmenorrhea, pelvic inflammatory disease, previous ectopic pregnancies, infection, possibly heart disease/anemia. IUDs can cause pain, bleeding, perforation, infection and pregnacy in spots where the fetus don’t fit.
The local endometrial reactions are well studied, the effect of progesterone is understood, the effect on sperm themselves to my knowledge was that of thickening the plug if progesterone is emitted by the IUD. I know zinc and copper have the same valencies but don’t understand why they would be induced to switch; no transporter exists, but it could indirectly effect the enzymatic reactions that occur to the zinc, which is outside of my league.