Neutron　powder-diffraction　studies　of　the　crystal　and　magnetic　structures　of　the　magnetocaloric　compound　Mn1.1Fe0.9(P0.8Ge0.2)　have　been　carried　out　as　a　function　of　temperature,　applied　magnetic　field,　and　pressure.　The　data　reveal　that　there　is　only　one　transition　observed　over　the　entire　range　of　variables　explored,　which　is　a　combined　magnetic　and　structural　transformation　between　the　paramagnetic　(PM)　and　ferromagnetic　phases　(T-c　approximate　to　255　K　for　this　composition).　The　structural　part　of　the　transition　is　associated　with　an　expansion　of　the　hexagonal　unit　cell　in　the　direction　of　the　a　and　b　axes　and　a　contraction　of　the　c　axis　as　the　FM　phase　is　formed,　which　originates　from　an　increase　in　the　intralayer　metal-metal　bond　distance.　The　application　of　pressure　is　found　to　have　an　adverse　effect　on　the　formation　of　the　FM　phase　since　pressure　opposes　the　expansion　of　the　lattice　and　hence　decreases　T-c.　The　application　of　a　magnetic　field,　on　the　other　hand,　has　the　expected　effect　of　enhancing　the　FM　phase　and　increasing　T-c.　We　find　that　the　substantial　range　of　temperature/field/pressure　coexistence　of　the　PM　and　FM　phases　observed　is　due　to　compositional　variations　in　the　sample.　In　situ　high-temperature　diffraction　measurements　were　carried　out　to　explore　this　issue,　and　reveal　a　coexisting　liquid　phase　at　high　temperatures　that　is　the　origin　of　this　variation.　We　show　that　this　range　of　coexisting　phases　can　be　substantially　reduced　by　appropriate　heat　treatment　to　improve　the　sample　homogeneity.