The Escort ZR3 laser shifter is neither an active or passive jammer. It "phase shifts" the laser to it has trouble bouncing back. Detectors can't tell how far away a laser trap is, so they phase shift the laser instead.
Two laser shifters won't interfere with one another, and may, in fact, disrupt a laser pulse even more.
The ionic charge on the zirconium ion in zirconium oxide (ZrO2) is +4. This is because oxygen typically has an oxidation state of -2, so with two oxygen atoms in ZrO2, the zirconium ion must have a charge of +4 to balance the overall charge of the compound.