If deuterons could fuse with other deuterons in a metal lattice, this would have been seen ages ago, just by accelerating deuterons into a deuterium-loaded material. This is how neutron generator tubes work, and they've been used for longer than you've probably been alive.
What happens in these tubes is the vast majority of deuterons lose energy by ionization and don't undergo nuclear reactions. There is no radical increase in fusion from electron shielding.
Just maybe people wanting a neutron source stay with thin foils to let the neutrons out because that's what they want. I wouldn't be surprised if this method of initiating fusion we completely overlooked for 90 years, but turns out to be viable after all. There are still many questions to be answered since the probability of a fusion event still seems to be too low. I just wish people would do more searching for answers and less outright rejection.
> In 1989, two electrochemists, Martin Fleischmann and Stanley Pons, reported that their apparatus had produced anomalous heat ("excess heat") of a magnitude they asserted would defy explanation except in terms of nuclear processes. They further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium. The small tabletop experiment involved electrolysis of heavy water on the surface of a palladium (Pd) electrode. The reported results received wide media attention and raised hopes of a cheap and abundant source of energy.
I planned to set up a similar experiment and bombard a hydrogen loaded target with muons, or move the experiment to the top of a Carpathian mountain, but the institute of nuclear research in Kharkiv, Ukraine is under attack, so it's not possible.
The idea of using ErD3 instead of Nickel or Palladium is very good, because it saves weeks of time to load the target with Deuterium.
Physicists knew P&F's nonsense was garbage because it required multiple miracles (that fusion would occur, that the ordinary fusion reactions would not, that some weird non-standard fusion reaction would occur instead.) Far, far more likely was they just were bumblers. And when replication failed (and it did fail; other vaguely similar but different sporadic results are not "replication") that prior was validated.